Push the rear sight detent down with a punch, then simply slide the rear sight to the left and off of the dovetail. Without the detent pushing up against the rear sight screw, the sight will come off easily. Then, carefully and slowly let the detent up. It's spring-loaded, so if you let it go suddenly, you'll put the detent and its spring into orbit, never to be found again. The screw in the rear sight is reverse-threaded. You turn it clockwise to remove it. When installing the Meprolights, first put the rear sight in the dovetail to make sure it fits. If not, first try removing some metal from its base with a fine file. Once it fits, put the original rear sight screw into the Meprolight sight, turning counter-clockwise, until it is almost flush with the right side of the slide. Put the rear sight into the dovetail, from the left side, about 3/4 of the way to the left. Make sure that a flat side of the rear sight screw is parallel to the ground, because the spring-loaded detent will catch this. Push in the spring-loaded detent with a punch, and move the rear sight further to the right so that the rear sight screw is aligned with the notch in the detent. Let the detent up slowly.