Theoretically, you just remove the nut in the center of the pulley and the pulley will come off. In the real world, that nut is freakin tight! To unscrew the nut, you have to keep the pulley from spinning, so you can jam a screw driver into one of the holes in the pulley and try to jam it. Best would be to remove the whole thing from the truck and stick it in a vice. Even then, you'll probably need a long breaker bar or some air tools.