They are pressed into place and will require pressing out or a heavy hit with a 5 lb sledge. Place a socket under the head (seat tracks upside down while doing this), then thread a nut onto the stud so the end of the stud is flush with the face of the nut. With the track supported by the socket (which will be large enough to allow the stud's head to fit inside when pounde out), give it a square, solid hit with the sledge while holding the socket in place.