Not sure about your car but most other cars you just hit the old stud with a sledge hammer from the outside which will force the stud out the back of the axle, the studs are on a spline which stops them from turning when you tighten the wheel nuts.
when you replace the damaged stud with the new one you just push it in from the back locating the spline slightly, place the nut on the stud and tighten it, this will pull the stud into place
hope this helps