First, you're going to want to assume the ball joints are corroded in. So get some WD-40 or some sort of penetrant. Soak the joints before you get started.
Now, once you have the wheel off the ground, and the spindle pulled off. It's ideally just a matter of putting a ball joint press on it and pushing it out of the A-arm and pushing the new one in. (Places like AutoZone rent these if you don't own one.) Go to it just how the Haynes manual should describe.
But, I've seen these presses bend and fail. So here's what I did.
-With that corner of the truck already lifted, put a jack under the A-arm and crank it up to brace it.
-Take a good solid hammer, not a mallet and beat the old ball joint out. It's gonna take some balls to get it out, so hit it like you mean it. !Safety goggles! and maybe even some hearing protection is recommended! Take car not to smash any edges.
-Clean up the journal the joint goes into.
-Let down the jack, THE ONE ON THE A-ARM, NOT THE ONE HOLDING UP THE TRUCK.
-Now you're going to need a good strong metal tube or socket that will fit around the joint and on to the lip of ball joint. And deep enough so it rests on the lip.
-Place joint in socket/tube. Put joint/socket on jack. Press up into the A-arm.
-Making sure your joint is set up straight against the journal.
-Take that hammer up again and beat the A-arm down around and onto the joint. Again, take care not to smash any edges or corners. You may even want to put a strong piece of wood between the arm and hammer.
Move slow at first. Little by little until you're positive the joint is going into the journal proper and not crooked.
-Smash it down until the A-arm is firmly against the lip on the ball joint.
-Repeat on other side.
Hope that was good enough.
This is not necessarily the proper way to do it, but it will get the job done.