screw from the ball joint. there is a metal piece inside the mirror that the screw threads into. if you do, it will fall out of position, and you will never get the screw threaded back into it. i did this on my first mirror replacement attempt. just loosen the screw and use a little force to pull the base from the mirror and use some force to push the new mirror onto the z mounting base. i hope this helps someone looking to replace their old mirror with one that isn't blackening around the edges.