The Kelsey-Hayes Disk Brake Swap Thread

With the proper square-ish socket, it should unscrew fairly easily (standard right-hand thread). As mentioned, best to do this w/ UCA in the car to hold it secure. Be very careful when re-installing to get the threads started right. You can easily strip the "threads" in the UCA since they were just self-cut as the ball joint was originally installed. Don't over-tighten or you will strip them. If you do, most people secure the new ball joint w/ a few spot welds, which you could later grind off to remove. Of course, check that wasn't already done on your car.

Other tips:

If the ball joint is still tight, I would just re-grease it and install a new boot. I use polyurethane boots (Energy Suspension), even in place of the rubber one that comes w/ a new ball joint. The upper ball joint sees minimal force so should last forever if kept dry and greased.

If replacing the bushings (most common wear item), look at Moog offset bushings to get the greater caster needed for radial tires. Don't orient them per the instructions, search here. You can use bolts, sockets and nuts to press in and out (search)

If removing the UCA, it would be pure gomer to not de-rust and paint.

When adjusting, try to get the most caster you can, while keeping the camber suitable (tire vertical). You want the lower ball joint as far forward of the upper as you can get, so the line between them strikes the road in front of the tire patch. This means rear UCA bushing as far in as you can, then adjust front for camber. Racers like negative camber (tire leaning in at top), like an Indy Car, though factory spec was slight positive camber. Straight vertical isn't bad and gives less tire wear. Search for Ehrenberg's article on alignment. For sure get toe-in correct or tires will quickly wear and/or car will wander on the highway.