How to Edit GridView Row using RadioButton in ASP.Net

Hi , iam using an grid in which inside the item template(the first one in which radio button is there). i use link button instead of radiobutton ,when i click on it iam able to edit as the textbox appears, but if i use the radio button,that editing option is not coming;

aspx:

<div id="banner" style="background-color: #00FFFF">

        </div>
    <div id="loginblock">
        <table>
            <tr>
      <td>UserName:</td>
                
                <td>
    <asp:TextBox ID="username" runat="server" onBlur="txtvalidation();" AutoPostBack="true"></asp:TextBox>
          </td>
                <td>
                    <div id="warning" style="color:aqua;width:100px" runat="server">
                        
                    </div>
                    <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ErrorMessage="PlS Enter Password" ControlToValidate="pwd"></asp:RequiredFieldValidator>

                </td>
                </tr>
            <tr>
                <td>Password:</td>
                <td>
     <asp:TextBox ID="pwd" runat="server" TextMode="Password" ></asp:TextBox>
                    </td>
                </tr>
            <tr>
                <td>
                    <asp:Button ID="btnLogin" runat="server" OnClick="btnLogin_Click" Text="Button" />
        </td>
                </tr>
            <tr>
                <asp:GridView ID="grd" runat="server" OnRowEditing="selectrd_CheckedChanged"  AutoGenerateColumns="false" DataKeyNames="userid">
              <Columns>
                  <asp:TemplateField HeaderText="edition">
                 <ItemTemplate>
                 <asp:RadioButton ID="rdnselect" runat="server"   CommndName="edit" />

                 </ItemTemplate>
                  </asp:TemplateField>
               <asp:BoundField HeaderText="ids" DataField="userid" />
                  <asp:TemplateField HeaderText="password">
                      <ItemTemplate>
                          <%# Eval("pwd") %>
                      </ItemTemplate>
                      <EditItemTemplate>
                          <asp:TextBox ID="edits" runat="server"   Text='<%# Eval("pwd") %>'></asp:TextBox>
                      </EditItemTemplate>
                  </asp:TemplateField>
              </Columns>
                </asp:GridView>

cs:
 protected void selectrd_CheckedChanged(object sender, GridViewEditEventArgs e)

    {
      
        grd.SelectedIndex = e.NewEditIndex;
        ldgrid();

    }

here if we remove the radiobutton and insert link button,onclick of the link button we can edit the values,pls say me how to do the same operation with the radio button.