I use a pair of locking needle nose pliers, however, I don't let them lock on the rod end... Grip the rod end where the turnbuckle goes in so that you are gripping the plastic over the metal.... this way it won't crush, and it allows you to add more pressure if you find the pliers slipping. Next, rotate the pliers the same as you would as if you are making a turnbuckle adjustment. The sucker should pop right off.
I replace my rod ends (ball cups) whenever they are showing excessive wear, or when one pops off. I usually replace all of them at once, as they are all probably worn to some extent. It also keeps the chassis nice and tight.
Speed Merchant Rev7, Tekin, TQ Racing (wire), Team Tamale
RC Excitement - Buy where you race, support your local tracks.