how to change the password by supplying old password and how to match newpassword and confirm password are same or not

You can use ASP.NET in built Controller to validate matching password

on button click you have to check whether old password is match or not

if old password match then you can change password Using sql query

and for matching password you can use ASP.NET CompareValidator....

Code for Match password...

Password:  <asp:TextBox id="TextBox1" runat="server"  TextMode="Password"></asp:TextBox>

Confirm Password: <asp:TextBox id="TextBox2" runat="server" TextMode="Password"></asp:TextBox>



            <asp:CompareValidator id="CompareValidator1"

             runat="server" ErrorMessage="Passwords do not match!"

             ControlToValidate="TextBox2"

             ControlToCompare="TextBox1" ></asp:CompareValidator>