We just did that yesterday, it's real easy, especially if you have the 2-piece control arms - the upper control arm consists of two halves, an inner half that's bolted to the frame and that you don't mess with at all, and an outer half that has the ball joint itself pressed in it and that you replace as a set.

First lift the truck by the lower control arm, this will keep the torsion bar loaded and will save you grief later on. Then when you pull the wheel and look at the upper control arm you'll see two big nuts staring you right in the face - these two hold the outer half of the control arm to the inner half that's bolted to the frame, they take 21mm (you can also use 13/16") socket. If you remove these two nuts, the outer half of the control arm will slide right out, it literally takes only a minute. However, watch out cause the whole knuckle assembly (wheel hub and brake too) will try to swing your way some, you may wanna prop that up with a piece of wood or something, or better yet have a helper hold it for ya. Then you'll have to separate the ball joint stud from the steerig knuckle: right below where the ball joint enters it you'll see a 10mm bolt going front<->rear through the knuckle, both its head and its nut take 15mm sockets/wrenches - remove the nut on the back side (facing the rear of the truck), pull the bolt out towards the front of the truck, put a pickle-fork tool between the knuckle and the ball joint and smack it a few times with a hammer and the ball joint will pop loose.

Then installation is reverese - slide new ball joint assembly onto the inner half of the control arm (watch out for the slot in the front corner of the new part, there's a bolt on the inner half of the control arm that's used for alignment purposes that it will have to slide on, you'll see what I mean when you get to it) and run the big nuts back on, then wiggle the ball joint's stud around till it matches the bore at the top of the knuckle and slide it down in it all the way (a crow bar helps for that somewhat, but may not be neaded) and then put the new cross bolt through the knuckle. put the new nut on the rear of that bolt, tighten everything up, put your wheel back on, drop her down, and head out for alignment.

Notice during that process you never mess with the torsion bar, heck you leave it alone even if doing the lower ball joint too - that's the beauty of torsion bar suspension, it not only rarely gets in your way, but sometimes even helps you.