title: how do i change a file extension on qt
body: <p>I have a piece of code to download a file from server. However, due to server constraint, I can not put .exe file at server. So I rename my XXX.exe file to XXX.alt(just a random extension) and put it on server. 
  Now my code can download XXX.alt, but how can I change the file name from XXX.alt back to XXX.exe when in QT environment?</p>