How to update multiple images and when on click on edit button if we have not selected the image how to save old image

here is the code
aspx page
<%@ Page Title="" Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true" CodeFile="ProductDetail.aspx.cs" Inherits="ProductDetail" %>
<asp:Content ID="Content1" ContentPlaceHolderID="head" Runat="Server"> </asp:Content> <asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server"> <asp:GridView ID="GVProductDetail" runat="server" DataKeyNames="Id" AutoGenerateColumns="False" CssClass="Gridview" HeaderStyle-BackColor="#4B6D9D " OnRowCancelingEdit="GVProductDetail_RowCancelingEdit" OnRowDeleting="GVProductDetail_RowDeleting" OnRowEditing="GVProductDetail_RowEditing" OnRowUpdating="GVProductDetail_RowUpdating" > ...