Hello and thank you for using just answer!
You mentioned the compressor.....are you trying to replace a specific belt here or all of them?
Ok, look down under the truck where the a/c belt rides, you will see a idler pulley that this belt rides between the compressor and the crank pulley. Take a 14mm wrench and break loose the center nut that holds this pulley on (just one turn), now on the bottom of this pulley you will see a longer 14mm bolt that this pulley is adjusted by, basically the center nut of this pulley locks the pulley in position on the adjuster bolt, so loosen the jam nut and then back off this adjuster and the belt can be serviced. These parts do commonly rust and break so prepare yourself for replacing them if you are in an area of rust/corrosion.