Well you can open it, but you have to be extremly careful, and not touch anything. If you touch a capacitor, it could send acid everywhere, or give you a huge electric shock. Before opening it, turn off your power at the mains, and press the power button on the case, that will drain excess power. but still don't touch anything. (I do not recomend opening up the PSU.)
To change it, if you have a custom built PC, then you can just pick up a ATX one (assuming you have a ATX case and a 20pin motherboard.) and unplug everything on the old one, take out the screws at the back, have a friend handy to hold the PSU, and remove it. (may need the heatsink taken off of the CPU. On my case it was a tight squeeze to get it out, with the heatsink in
place. Get the new PSU, get a friend to hold it in place, and screw it in. put all the ires in the slots.
You can get a brush to clean it I believe (I assume a special one?) But just ground your self, and loosen it carefully with your fingers. (remain grounded though.)
Cisco CCNA, Comptia A+, 1/3 through CCNP