Open CuteSoft_Client\CuteEditor\Dialogs\InsertFlash.aspx and modify the following code:

 

   protected override void GetFiles(ArrayList files)
    {
        files.AddRange(fs.GetFileItems(CurrentDirectory, secset.FileNamePrefix + "*.swf"));
    }
    protected override bool AllowFileName(string filename)
    {
        filename = filename.ToLower();
        return filename.EndsWith(".swf");
    }