Asumeing it is a standard fan with mounting holes on both sides you can simply open up the power supply and flip the fan around.
Warning!! this will void your PSU warrenty and is potentially dangerous if you don't know what your doing. I reccomend you unplug the PSU from AC and hit the power button on the computer to drain the capacitors before opening the unit and still be carefull when inside.
I'm not firmiliar with that brand of psu so I don't know how good the quality of the unit is.