It is not too difficult once you see how it is done. Check the manual for a description. In short you need to press and hold the chamber end of the barrel down when simultaneously pulling the slide to the rear when replacing the slide so that the barrel "catches" and does not slide back too far. If you do not see the muzzle starting to protrude out of the front of the slide, you are in trouble. Stop and start again. I find inserting an empty magazine before replacing the slide helps. Go slow and practice once or twice and you will get it.