This particular vehicle is a 2005 GMC Sierra 2500 with a 6.0L gas engine.
Tools and parts needed. Remove the engine cover using an 8mm or 5/16″ socket. Using the same socket, loosen the air housing which attaches the air housing to the throttle body. Move the air housing out of your way enough to access the belts. Using a 15mm socket with ratchet or a 15mm drive belt removal tool and loosen the tension of the belt tensioner in order to remove the drive belt. The secondary air conditioning belt is worn out and needs replacing also. This belt tensioner simply uses the end of a 3/8″ ratchet to release the belt tensioner. Re-install both belts in the reverse order of removal. Most vehicles will have a belt routing diagram located somewhere above the radiator or on the hood. Start the vehicle and make sure the belt(s) is riding on each pulley correctly and there is no belt squeak. Congratulations, you just replaced your own belts and saved yourself some money.