did you remove the old ball joint?
if not, there is a C-clip that holds in place. remove the C-clip and then press the ball joint out, or hammer it out.
before you press the new one in make sure you clean the control arm good, maybe with some 1000grit sand paper, just to remove any surface rust and to make it smooth for the new ball joint.
then press it in by hand as much as you can. then put a big socket on top of it (i use the one that i take the axle nut off with...i think its a 32mm) and put in the press or hammer it with the hammer. after its all the way in put the new C-clip on and you're done.
