How to change break fluid - 2002 GMC Sierra

Usually there's no need for a fluid change on the brakes unless you contaminated it with something. However, if you must, then you want to use two people. Start with the rear brakes. Go to one side, remove the wheel, and you'll see a little nub looking thing on the back of the backing plate. It should have a rubber cap on it, but that may have come off. Use a box ended wrench or a socket to loosen it, but do not remove it. Have a partner press on the brakes. Fluid will come out, and tighten before having your partner let up on the brakes. Do this until your brake fluid reservoir is ALMOST empty. At this point, have your partner wait to let up on the pedal, and go up to the front of the truck with your new brake fluid. As your partner lets up on the pedal slowly, exactly as the fluid runs out, start pouring and fill it up. Continue with the first activity of pumping(just don't run out of fluid at any point after this) until you see the new fluid coming out. Close off that valve, and move to the other side. Do the same, only you don't need to let it run out. The front brakes are done the same way.