Rename .xml file to .xls

Question

Hi

  I have below code . I want if file has file extendsion .xml then first it should be saved as .xls with same name

string FolderPath = "~/Upload/ExcelUpload/";
                    string FilePath = Server.MapPath(FolderPath + RandomName + FileName);

                    FileUpload1.SaveAs(FilePath);

Thanks