You have to completely unbolt the ball joint from the lower control arm. Can you get the nut off? If not, get a second hand in there, with maybe a crow bar or breaker bar, and push down on the lower control arm just enough to get the nut off the top of the ball joint. Then you have to push the lower control arm down while you pull the hub assembly up and off of the ball joint. Then, remove the circlip from the ball joint, did your new ball joints come with new circlips? The old ones will probably get bent out of shape when you pry them out.
Then take your ball joint press tool, and put one of those little pipes on the bottom, and loop the hole on the top over the ball joint and start cranking, it'll *pop* right out.
That is the exact same kit I rented from auto zone. I hope my explanation helps at least a little. Here's a rough MSpaint picture of what it should look like when you press the ball joint out.
You WILL require a second hand to hold the hub assembly out of the way for you.
edit: I had to take the axle nut off for this one. The best way to do that is remove the cotter pin, to put the wheel on (take off the center cap), stick your 32MM socket with a breaker bar on it, and push like hell on the breaker bar.