Three main options in ascending order of preference:
1. Hammer it out
2. Cut it out (cut the back/bottom off, hammer the ball and plastic insert out, thread a hacksaw through the body and carefully cut through the sidewall, then tap the rest out.)
3. Press it out
For options 1 and 3, you'll need appropriately sized backers. I can give you measurements if you want, or easy enough to measure. I went around my garage and the drill press, bike stand and exercise bike are now all 3 inches shorter.
I opted for number 2 the first time I did the job. I built a press so now, always option 3. A garage should charge you no more than 1/2 hour labour (£20-30) if you take the wishbones with the old balljoints still in, and new balljoints).