How do I download a specific file which was saved in a specific folder of the application

if (FileUpload1.HasFile)
            {
                if (FileUpload1.PostedFile.ContentLength / 1024 > 2048)
                    throw new ApplicationException
                    ("Uploaded File Should less then 2MB");
                filename = FileUpload1.PostedFile.FileName;
                FileUpload1.SaveAs(Server.MapPath
                ("~/FILE_UPLOADS/ARREST_MEMO/ ") + (filename));
                Regex FilenameRegex;
                FilenameRegex = new Regex("(.*?)\\.(pdf)$", 
                                RegexOptions.IgnoreCase);
                if (!FilenameRegex.IsMatch(filename))
                    throw new ApplicationException("Browse PDF files Only");
            }

try
            {
                filename = UpName.Value.ToString();
                filepath =
                type = System.IO.Path.GetExtension(filename);
                Byte[] bytes = Convert.FromBase64String(UpData.Value);
                //Response.Clear();
                //Response.ClearHeaders();
                Response.Buffer = true;
                Response.Charset = "";
                this.EnableViewState = false;
                Response.Cache.SetCacheability(HttpCacheability.NoCache);
                Response.ContentType = "Application/pdf";
                //Response.AddHeader("Content-Disposition", 
                                     "attachment;filename=" + filename);
                Response.AppendHeader("Content-Disposition", "attachment; 
                                 filename=" + Path.GetFileName(filepath));
                Response.TransmitFile(Server.MapPath(filepath));
                Response.BinaryWrite(bytes);
                Response.Flush();
                Response.End();
                HttpContext.Current.ApplicationInstance.CompleteRequest();
            }