Copy files only if changed / newer / modified / updated using C# .Net

Here I am cheking the file Length if the destination file exists.

HTML

<asp:Button Text="Copy Files" OnClick="CopyFiles" runat="server" />

Namespace

using System.IO;

C#

protected void CopyFiles(object sender, EventArgs e)
{
    string[] files = Directory.GetFiles(Server.MapPath("~/Folder1/"));
    foreach (string file in files)
    {
        if (Path.GetFileName(file) == "Hello.txt" || Path.GetFileName(file) == "Hi.txt")
        {
            if (File.Exists(Server.MapPath("~/Folder2/") + Path.GetFileName(file)))
            {
                FileInfo fileInfoSource = new FileInfo(file);
                FileInfo fileInfoDest = new FileInfo(Server.MapPath("~/Folder2/") + Path.GetFileName(file));
                if (fileInfoSource.Length > fileInfoDest.Length)
                {
                    File.Copy(file, Server.MapPath("~/Folder2/") + Path.GetFileName(file), true);
                }
            }
            else
            {
                File.Copy(file, Server.MapPath("~/Folder2/") + Path.GetFileName(file));
            }
        }
    }
}