remove the rotors, and brake caliper, you prolly have to remove the dust shield as well, more or less strip everything off the hub. once the shield is off you will see where the studs are pressed in. just hammer the old one out and replace with a new one, about 7-11 dollars.
just make sure you hammer it out strait, dont want to warp the hole. and when putting the new one in, do not hammer it in, place the rotor over the studs, put the wheel back on and put 2 lug nuts back on, use the third lug nut and tighten it slowly to pull the stud into place. torque to 80 ft pounds or so, then un torque. remove the wheel and rotor again and see if its seated flat. once its secured replace all the removed hardware.
its not the end of the world... thats how i busted off my wheel locks when i lost my key.
Torinalth