Make sure that the cylinders do need to be replaced. Perhaps you only need to lubricate. To do this, take the key, dip it in engine oil, insert it in the lock, and scroll a few times. If he began to rotate smoothly, so the problem is resolved.
If the lubrication did not help, the larva will have to be replaced.Have mortise lock and remove end plate middle screw located parallel to the cylinders. Insert the key and rotate it into a position in which the mechanism can be removed. Remove it. Screw save.
Slip the lock will have to be removed from the door. Having done this, Unscrew the two screws that secure the striker to the lock body and remove it. These screws will also save.
Removed a larva take to the hardware store, putting in a door attendant who will be on duty while it is open. If not, do this: take a picture of the mechanism next to a ruler, and then install it in place. If the lock mortise, screw the Central screw, and if the invoice that you install it on the door. To the store take phone or camera with a photo of the larvae, or a printout of this picture.
Ask the seller to pick up instead of liczniku, a verified manufacturer. Be sure to ask what material is made the mechanism. If he silumin, give up buying and go to another store.
By purchasing and bringing home the larva, remove the old if it is still in the castle. If mortise lock, turn the key to the position where to insert the mechanism into the hole, insert it there, and then fix the Central screw in the end plate. To overhead lock screw larva with two screws, and then install it on the door.
Make sure that the lock works properly without closing the door. Then close and repeatedly lock and unlock it. Now the lock can be used.New larva has a long handle it carefully. Do not force when inserting, removing and turning the key. Regularly lubricate the mechanism in the manner described in step 1. Never lubricate the lock in other ways (for example, by pouring oil directly into the well).