Loosen bolts that hold the bracket with the ball joint to the arms. Remove cotter pin, remove nut and washer, partially reinstall nut, hammer the fuck out of the ball joint with a drift and bfh.
It helped mine to have the rear axle Hanging with no truck weight on it.
Mine took 10-15 good swings and it popped free. Some people also use a large wedge pickle fork where the rubber boot is and swing for the fences..mine didn't need the pickle Fork but then front steering ball joints did.
------ Follow up post added June 16th, 2016 05:35 PM ------
Edit: I also replaced mine with a whole new ballpoint and bracket from gwen Lewis UK. Is greaseable, no pressing out the old one, and has better articulation.