1. Access the preferences pane.
   
   Keyboard shortcut: Command key (it has a ⌘ symbol) and then the ","
   
   
   
   
2. Click the General, then in the Date/Time format section's Time popup, choose the format your prefer:
   
   
   
   

If you don't see the format you would like, please let us know and we will try to add it in a future update.