Capacitors store a charge, which can shock you. The ones on this board are relatively small and should be harmless, but to be on the safe side leave it unplugged for 24 hours and consider using a capacitor discharge probe or multimeter set to current measurement to discharge them.

Remove 3 Short Philips screws and 1 large Philips screw with washer (marked *) to release the PSU board. It pulls upwards a little off the standoffs and directly away from the connector to the logic/i/o board.