You can reverse the axis by checking or unchecking the Dir Low Active setting but this can have adverse effects on some drives, wont harm them but they just wont work properly.
Your other option is to go to the Config Menu then down to System HotKeys, click on the Z++ press the Pg Up on your keyboard, then do the same for the Z-- this time pressing the PgDn key. This will reaign the keyboard buttons the correct way for you.
Hood