How can i redirect to login page, if user access is wrong

protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                if (Session["UserId"] != null)
                {
                    Session.Clear();
                    Session.RemoveAll();
                    Session.Abandon();
                }
            }
          }
       

        protected void btnLogin_Click(object sender, EventArgs e)
        {
            string str1 = null;
            string[] UserName = null;
            try
            {
                if (txtusername.Text.Contains("@"))
                {
                    string str = txtusername.Text;
                    UserName = str.Split('@');
                    LoginBL.UserName = UserName[0].ToString();
                    str1 = UserName[0].ToString();
                }
                else
                {
                    LoginBL.UserName = txtusername.Text.Trim();
                    str1 = txtusername.Text.Trim();
                }
                LoginBL.Password = txtpassword.Text.Trim();
                string Role = LoginBL.GetUserLogin();

                if (Role == "NoUser")
                    lblMessage.Text = "User Name and password mismatch. Try again.";
                else
                {
                    Session["UserId"] = LoginBL.UserId;
                    Session["Emp_Cus_Id"] = LoginBL.Emp_Cus_Id;
                    if (Role == "Admin")
                    {
                        Session["UserName"] = str1;
                        Response.Redirect("~/Admin/AdminHome.aspx");
                        //FormsAuthentication.RedirectFromLoginPage("Admin", false);
                    }
                    else if (Role == "Employee")
                    {
                        Session["UserName"] = str1;
                        LoginBL.ActiveEmployeeOnlineStatus(Convert.ToInt32(Session["Emp_Cus_Id"]));
                        Session["UserType"] = "Employee";
                        Response.Redirect("~/Employee/EmployeeHome.aspx");
                        //FormsAuthentication.RedirectFromLoginPage("Employee", false);

                    }
                    else if (Role == "Customer")
                    {
                        Session["UserName"] = str1;
                        LoginBL.ActiveCustomerOnlineStatus(Convert.ToInt32(Session["Emp_Cus_Id"]));
                        Session["UserType"] = "Customer";
                        Response.Redirect("~/Customer/CustomerHome.aspx");
                        //FormsAuthentication.RedirectFromLoginPage("Customer", false);
                    }
                }
            }
            catch (Exception ex)
            {
                lblMessage.Text = ex.Message;
            }

Load

if (Session["UserId"] == null || Session["Role"] == null
    || !Session["Role"].ToString().Equals(EnumUserRoles.Admin.ToString(), StringComparison.InvariantCultureIgnoreCase))
{
    arAdminHome.Visible = false;
    Response.Redirect("../LogIn.aspx");
}