how to edit ,delete,update,cancel in a gridview using C#

SlNo	       int	        Unchecked
WebsiteName     varchar(100)  	Unchecked
PortId	       varchar(100)	Unchecked
Createdate  	date	        Unchecked

<asp:GridView ID="gvDetails" DataKeyNames="SlNo,Websitename" runat="server"
AutoGenerateColumns="false" CssClass="Gridview" HeaderStyle-BackColor="#61A6F8"
ShowFooter="true" HeaderStyle-Font-Bold="true" HeaderStyle-ForeColor="White"
onrowcancelingedit="gvDetails_RowCancelingEdit"
onrowdeleting="gvDetails_RowDeleting" onrowediting="gvDetails_RowEditing"
onrowupdating="gvDetails_RowUpdating"
onrowcommand="gvDetails_RowCommand">
<columns><asp:TemplateField><edititemtemplate>
    <asp:Button ID="BtnUpdate" CommandName="Update" runat="server" ToolTip="Update" Height="20px" Width="20px" Text="update" />
<asp:Button ID="BtnCancel" runat="server" CommandName="Cancel"  ToolTip="Cancel" Height="20px" Width="20px" Text="Cancel"/>
</edititemtemplate><itemtemplate>
 <asp:Button ID="BtnUpdate" CommandName="Update" runat="server" ToolTip="Update" Height="20px" Width="20px" Text="update" />
    <asp:Button ID="BtnCancel" runat="server" CommandName="Cancel"  ToolTip="Cancel" Height="20px" Width="20px" Text="Cancel"/>
</itemtemplate><footertemplate>
<asp:Button ID="btnAdd" runat="server"  CommandName="AddNew" Width="30px" Height="30px" ToolTip="Add new User" ValidationGroup="validaiton" />
</footertemplate><asp:TemplateField HeaderText="SlNo"><edititemtemplate>
<asp:Label ID="lbleditusr" runat="server" Text=' <%#Container.DataItemIndex+1%> '/>
</edititemtemplate><asp:TemplateField HeaderText="SiteName"><edititemtemplate>
 <asp:LinkButton ID="LinkButton1" runat="server" CommandName="redirect" Text='<%# DataBinder.Eval(Container.DataItem, "WebsiteName")%>'  ToolTip="redirect"></edititemtemplate><itemtemplate>
 <asp:LinkButton ID="LinkButton1" runat="server" CommandName="redirect" Text='<%# DataBinder.Eval(Container.DataItem, "WebsiteName")%>'  ToolTip="redirect"></itemtemplate><footertemplate>
<asp:TextBox ID="txtsitename" runat="server"/>
<asp:RequiredFieldValidator ID="rfvsitename" runat="server" ControlToValidate="txtsitename" Text="*" ValidationGroup="validaiton"/>
</footertemplate></columns>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Configuration;
using System.Data.SqlClient;
using System.Data;
using System.Drawing;
public partial class gridview_testing : System.Web.UI.Page
{  
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            string sqlCon = ConfigurationManager.ConnectionStrings["cnstr"].ToString();
            SqlConnection con = new SqlConnection(sqlCon);
            BindEmployeeDetails();
        }
    }
    protected void BindEmployeeDetails()
    {
        string sqlCon = ConfigurationManager.ConnectionStrings["cnstr"].ToString();
        SqlConnection con = new SqlConnection(sqlCon);
        con.Open();
        SqlCommand cmd = new SqlCommand("select WebsiteName from Websitedtls", con);
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        DataSet ds = new DataSet();
        da.Fill(ds);
        con.Close();
        if (ds.Tables[0].Rows.Count > 0)
        {
            gvDetails.DataSource = ds;
            gvDetails.DataBind();
        }
        else
        {
            ds.Tables[0].Rows.Add(ds.Tables[0].NewRow());
            gvDetails.DataSource = ds;
            gvDetails.DataBind();
            int columncount = gvDetails.Rows[0].Cells.Count;
            gvDetails.Rows[0].Cells.Clear();
            gvDetails.Rows[0].Cells.Add(new TableCell());
            gvDetails.Rows[0].Cells[0].ColumnSpan = columncount;
            gvDetails.Rows[0].Cells[0].Text = "No Records Found";
        }
    }
    protected void gvDetails_RowEditing(object sender, GridViewEditEventArgs e)
    {
        gvDetails.EditIndex = e.NewEditIndex;
        BindEmployeeDetails();
    }
    protected void gvDetails_RowUpdating(object sender, GridViewUpdateEventArgs e)
    {
        string sqlCon = ConfigurationManager.ConnectionStrings["cnstr"].ToString();
        SqlConnection con = new SqlConnection(sqlCon);
        int SlNo = Convert.ToInt32(gvDetails.DataKeys[e.RowIndex].Value.ToString());
        string sitename = gvDetails.DataKeys[e.RowIndex].Values["SiteName"].ToString();
        TextBox txtsitename = (TextBox)gvDetails.Rows[e.RowIndex].FindControl("txtsitename");
        con.Open();
        SqlCommand cmd = new SqlCommand("update Websitedtls set WebsiteName='" + txtsitename + "' where SlNo=" + SlNo, con);
        cmd.ExecuteNonQuery();
        con.Close();
        lblresult.ForeColor = Color.Green;
        lblresult.Text = sitename + " Details Updated successfully";
        gvDetails.EditIndex = -1;
        BindEmployeeDetails();
    }
    protected void gvDetails_RowCancelingEdit(object sender, GridViewCancelEditEventArgs e)
    {
        gvDetails.EditIndex = -1;
        BindEmployeeDetails();
    }
    protected void gvDetails_RowDeleting(object sender, GridViewDeleteEventArgs e)
    {
        string sqlCon = ConfigurationManager.ConnectionStrings["cnstr"].ToString();
        SqlConnection con = new SqlConnection(sqlCon);
        int SlNo = Convert.ToInt32(gvDetails.DataKeys[e.RowIndex].Values["SlNo"].ToString());
        string sitename = gvDetails.DataKeys[e.RowIndex].Values["sitename"].ToString();
        con.Open();
        SqlCommand cmd = new SqlCommand("delete from Websitedtls where SlNo=" + SlNo, con);
        int result = cmd.ExecuteNonQuery();
        con.Close();
        if (result == 1)
        {
            BindEmployeeDetails();
            lblresult.ForeColor = Color.Red;
            lblresult.Text = sitename + " details deleted successfully";
        }
    }
    protected void gvDetails_RowCommand(object sender, GridViewCommandEventArgs e)
    {
        string sqlCon = ConfigurationManager.ConnectionStrings["cnstr"].ToString();
        SqlConnection con = new SqlConnection(sqlCon);
        if (e.CommandName.Equals("AddNew"))
        {
            TextBox txtsitename = (TextBox)gvDetails.FooterRow.FindControl("txtsitename");           
            con.Open();
            SqlCommand cmd = new SqlCommand("insert into Websitedtls(WebsiteName) values( '" +txtsitename.Text + "' )", con);
            int result = cmd.ExecuteNonQuery();
            con.Close();
            if (result == 1)
            {
                BindEmployeeDetails();
                lblresult.ForeColor = Color.Green;
                lblresult.Text = txtsitename.Text + " Details inserted successfully";
            }
            else            {
                lblresult.ForeColor = Color.Red;
                lblresult.Text = txtsitename.Text + " Details not inserted";
            }}}}