文件后缀名改名？

我用下面的代码对一批文件的后缀进行改名。但就是没用，急呀！
String pathName , newExtention;
   try
   {
    foreach(FileInfo fileInfo in fileInfoList)
    {
     pathName =fileInfo.FullName;
     newExtention = "." +  newSuffix.Text;
     System.IO.Path.ChangeExtension( pathName ,newExtention);   
    }
   }
   catch(IOException ioExpecption){
    Console.WriteLine("The process failed: {0}", ioExpecption.ToString());
   }

请各位同仁赐教！
谢谢