I use a tool that looks like a fork, designed just for this job.
It is wedged in between the joint and steering knuckle and tapped
with a hammer.
Another tool designed just for this grabs on sort of like a big clamp
and allows you to push it out.
If you have an auto parts store nearby it would be a common tool
for them to lend.
This link has a good picture and discussion of removal:
Lower Ball Joint Replacement Question