Yeah. Just shut down, unlug the power. Hit the power button(lights should blink for a millisecond). Congrats your PSU caps are now drained(but still be careful).
I have changed PSU fans in the past with good success. Just make sure your new fan has a similar number of CFM's(cubic feet per minute or air) to the old one. You don't want to overheat your PSU. Once done load it up and check for stability(preferably with a multi-meter).
Hope this helps