How to replace the lock core of the old round-headed door lock

Methods: 1. First know the position of the screw hole of the lock core of the security door, unscrew the screw and write down the lock core of the security door. 2. Turn the key to a certain position, pull the fork in the lock cylinder groove, and pull out the whole lock cylinder from the lock body. 3. Know the size of the anti-theft lock, and buy the lock core with the same size on the market according to the size. 4. Replace the lock cylinder, then tighten the lock cylinder screw, and then install the inner and outer handles. There are two screw holes in the handle in the room, and then tighten the screws.