<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false" AllowPaging="true" DataKeyNames="AutoId">
            <Columns>
                <asp:TemplateField HeaderText="Select">
                    <ItemTemplate>
                        <asp:CheckBox ID="chkSelect" runat="server" />
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:BoundField HeaderText="AutoId" DataField="AutoId" />
                <asp:BoundField HeaderText="First Name" DataField="FirstName" />
                <asp:BoundField HeaderText="Last Name" DataField="LastName" />
                <asp:TemplateField HeaderText="Is Active?">
                    <ItemTemplate>
                        <%# Eval("Active").ToString().Equals("True") ? "Yes" : "No" %>
                    </ItemTemplate>
                </asp:TemplateField>
            </Columns>
        </asp:GridView>
        <p><asp:Button ID="btnDelete" runat="server" Text="Delete Selected Records" OnClick="DeleteSelectedRecords" /></p>

Code Behind

string _connStr = ConfigurationManager.ConnectionStrings["ConnStr"].ConnectionString;
protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        this.GetData();
    }
}
private void GetData()
{
    DataTable table = new DataTable();
    // get the connection
    using (SqlConnection conn = new SqlConnection(_connStr))
    {
        // write the sql statement to execute
        string sql = "SELECT AutoId, FirstName, LastName, Age, Active FROM PersonalDetail ORDER By AutoId";
        // instantiate the command object to fire
        using (SqlCommand cmd = new SqlCommand(sql, conn))
        {
            // get the adapter object and attach the command object to it
            using (SqlDataAdapter ad = new SqlDataAdapter(cmd))
            {
                // fire Fill method to fetch the data and fill into DataTable
                ad.Fill(table);
            }
        }
    }
    GridView1.DataSource = table;
    GridView1.DataBind();
}
protected void DeleteSelectedRecords(object sender, EventArgs e)
{
    Response.Write("<h3>Selected records</h3>");
    foreach (GridViewRow row in GridView1.Rows)
    {
        CheckBox chk = (CheckBox)row.FindControl("chkSelect");
        if (chk.Checked)
        {
            int autoId = int.Parse(GridView1.DataKeys[row.RowIndex].Value.ToString());
            // get the selected AutoId and cells text
            Response.Write("<p>AutoId: " + autoId + " deleted</p>");
            // fire your DELETE method from BAL or service layer
            using (SqlConnection conn = new SqlConnection(_connStr))
            {
                string sql = "Delete from PersonalDetail" +
                " where AutoId = @AutoId";
                using (SqlCommand cmd = new SqlCommand(sql, conn))
                {
                    cmd.Parameters.AddWithValue("@AutoId", autoId);
                    conn.Open();
                    cmd.ExecuteNonQuery();
                    conn.Close();
                }
            }
        }
    }
    // repopulate the fresh data
    this.GetData();
}