I guess that is just removing all the screws on the back side of the card and removing the exhaust bracket sometimes (depending on the model), just be sure to remove all the screws (about 15 depends on the card) if its hard to remove the cover check again cause must be some screw under a sticker or something.
 
just be patience and the probability of something goes wrong is very small. After the clean remember to aply TIM on the GOU and memories or get new memory pads (but difficult to find I guess).