i am having a grid and one of the column is checkbox and the header of the checkbox is used to select all

    <%@ Page Title="" Language="C#" MasterPageFile="~/home.Master" AutoEventWireup="true" CodeBehind="Home.aspx.cs" Inherits="employee_managment.Home" %>
     <asp:Content ID="Content1" ContentPlaceHolderID="head" runat="server">
    <link rel="stylesheet" href="https://code.jquery.com/ui/1.11.4/themes   /smoothness/jquery-ui.css"/>
    <script src="https://code.jquery.com/jquery-1.10.2.js"></script>
    <script src="https://code.jquery.com/ui/1.11.4/jquery-ui.js"></script>
    <link href="style.css" rel="stylesheet" />
       <script>
        $(function () {
        $("#tabs").tabs({ active: 1 });
        });
        function NewWindow(empid)//this is used to open the popup window
        {
        var Open=window.open("AddEmployeeWebForm.aspx?empid="+empid,"EmployeeDetailsTab","Height=800px");
        }
        function EditLink(EmployeeID)//when we click on this this employee popup is opened
        {
            var Edit = window.open("AddEmployeeWebForm.aspx?empid=" + EmployeeID, "EditingEmployee", "Height=800px");

        }//select all is used to select all the data in the grid
        function SelectAllCheckboxes1(chk) {

            $('#<%=EmployeeDetailsGrid.ClientID%>').find("input:checkbox").each(function () {
                if (this != chk) {
                    this.checked = chk.checked;
                }
            });
        }

        function DeleteConfirmbox(val) {//is to delete the selected data from grid
            var arrCheckboxes;
            var checkboxSelector = "input[type='checkbox']";
            $("body").delegate(checkboxSelector, "click", function () {
                arrCheckboxes = $(checkboxSelector).map(function () {
                    return this.checked;//
                }).get();
            });



            // confirm meg check for delete
            var result = confirm('Are you sure delete Emp Record?');
            if (result) {

                // this is for get hdnvalue id
                var value = val.replace("DeleteEmpData", "hdnEmployyeID");

                $.ajax({
                    type: "POST",//akax is used to delete data

                    url: "Home.aspx/DeleteEmpData", // this for calling the web method function in cs code.
                    data: '{EmployeeID: "' + $("#" + value).val() + '" }',// empid value
                    dataType: "json",
                    success: OnSuccess,
                    failure: function (data) {
                        alert(data);
                    }


                });

                return false;
            }
        }

        // function OnSuccess
        function OnSuccess(response) {
            return false;
            if (response.d == 'true') {


            }

        }


     </script>
      </asp:Content>
      <asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
      <asp:button id="backButton" runat="server" text="Back"OnClientClick="JavaScript:window.history.back(1);return false;" OnClick="backButton_Click"></asp:button>

      <div style="text-align:right">WELCOME{<asp:Label id="UserDetails" runat="server"></asp:Label>}</div>
      <div style="text-align:right"> <asp:Button CssClass="Button" ID="logout" Text="logout" runat="server" OnClick="logout_Click"></asp:Button></div>

     <div id="tabs" class="feature-tabs">//
        <ul>
                 <li><a href="#Client">Client</a></li>
                 <li><a href="#Employee">Employee</a></li>
       </ul>
          <div id="Client">
              <table style="height:500px">

        </table>

       </div>
      <div id="Employee">
      <table style="width:50%">//this is used to show the tabs button
      <tr>
            <td><asp:Button CssClass="Button"  ID="AddEmployee" Text="Add Employee" runat="server" OnClientClick="return NewWindow(0)" OnClick="AddEmployee_Click" ></asp:Button></td>
          <td><asp:Button  CssClass="Button" ID="DeleteEmployee" Text="Delete Employee" runat="server"  OnClientClick="javascript:DeleteConfirmbox();" ></asp:Button></td>
           <td><asp:Button  CssClass="Button" ID="Print" Text="Print" runat="server" OnClick="Print_Click" ></asp:Button></td>
          <td><asp:Button  CssClass="Button" ID="Refresh" Text="Refresh" runat="server" OnClick="Refresh_Click" ></asp:Button></td>

          </tr>

          </table>
            <br />
        <asp:GridView ID="EmployeeDetailsGrid" runat="server" AutoGenerateColumns="false" ShowHeaderWhenEmpty="true" DataKeyNames="EmployeeID" Width="100%" >
      <Columns>
          <asp:TemplateField>
              <HeaderTemplate>
                  <asp:CheckBox  ID="SelectAll"                                                                          onclick="javascript:SelectAllCheckboxes1(this);"runat="server">
             </asp:CheckBox>
              </HeaderTemplate>
              <ItemTemplate>
                  <asp:CheckBox ID="GridCheckBox" runat="server" />
              </ItemTemplate>
          </asp:TemplateField>
          <asp:BoundField DataField="EmployeeID"   HeaderText="ID" />
          <asp:BoundField DataField="SaveFirstName" HeaderText="Name" />
          <asp:BoundField DataField="SavePhone" HeaderText="Phone" />
          <asp:BoundField DataField="SaveZipCode" HeaderText="ZipCode" />
          <asp:BoundField DataField="Designation" HeaderText="Designation" />

          <asp:TemplateField HeaderText="Edit">
           <ItemTemplate >//hear will be the edit link
           <a href="#" id="EditLink" onclick="return EditLink(<%#Eval("EmployeeID") %>);">Edit</a>

           </ItemTemplate>
           </asp:TemplateField>

          </Columns>

       </asp:GridView>

      </div>


       <div style="height:500px"></div>
        </div>
        </asp:Content>



this is the code behind

    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Web;
    using System.Web.UI;
    using System.Web.UI.WebControls;

     namespace employee_managment
    {
    public partial class Home : System.Web.UI.Page
    {

        protected void Page_Load(object sender, EventArgs e)
        {
            try
            {
                if (!this.Page.IsPostBack)//hear we bind the data to list
                {
                    EmployeeDetails emp = (EmployeeDetails)Session["ActiveUser"];
                    if (emp != null)
                        UserDetails.Text = emp.EmployeeName;
                    DataAccess access = new DataAccess();
                    List<AddEmployee> GetDetails = new List<AddEmployee>();
                    GetDetails = access.GetEmployeeDetails();
                    EmployeeDetailsGrid.DataSource = GetDetails;
                    EmployeeDetailsGrid.DataBind();


                }
            }
            catch (Exception)
            {

            }


        }

        protected void logout_Click(object sender, EventArgs e)//this is used to terminate the session
        {
            Session.Clear();
            Session.Abandon();
            Response.Cache.SetExpires(DateTime.UtcNow.AddDays(-1));
            Response.Cache.SetValidUntilExpires(false);
            Response.Cache.SetRevalidation(HttpCacheRevalidation.AllCaches);
            Response.Cache.SetCacheability(HttpCacheability.NoCache);
            Response.Cache.SetNoStore();
            Response.Redirect("login.aspx");
        }

        protected void backButton_Click(object sender, EventArgs e)
        {
            Session.Clear();
            Session.Abandon();
        }

        protected void AddEmployee_Click(object sender, EventArgs e)
        {

        }

        protected void DeleteEmployee_Click(object sender, EventArgs e)
        {

        }

        protected void Print_Click(object sender, EventArgs e)
        {

        }

        protected void Refresh_Click(object sender, EventArgs e)//when we click on refresh we again bind the grid view data
        {
            try
            {
                    DataAccess access = new DataAccess();
                    List<AddEmployee> GetDetails = new List<AddEmployee>();
                    GetDetails = access.GetEmployeeDetails();
                    EmployeeDetailsGrid.DataSource = GetDetails;
                    EmployeeDetailsGrid.DataBind();
            }
            catch (Exception)
            {

                throw;
            }
        }
        [System.Web.Services.WebMethod]
        public static string DeleteEmpData(int EmployeeID)
          {



          }


         }
     }