this is how i demounted the old lock and mounted the new one:
First thing you do is remove the lock cover which is held by a rivet. Use a flat screwdriver to lift the cover. If you work carefully, you can use the rivet again later.
Now you drill out the old lock. I f you still have the original keys, use them to pull the lock outside. But hardly anyone who changes a lock will have the keys of the original one. So what you do is take a drill (6) and start drilling. The cylinder's material is pretty soft so any steel drill should do the job.
Handy people might also manage to break the tumbler in the lock's upper region with some well aimed hits. Make sure not to damage the seat of the lock. Pull the drill out every now and then and blow away the particles. Eventually the lock will give in. In case it won't fall right into your hands, drill a Spax into the cylinder and use pliers to pull it out. The springs and the dirt need to be removed too.
No it's very easy to mount the new lock. Use some grease on spring and lock and mount it. Mount the cover with the rivet, turn the key and there you go. Here are some pictures of how I de/mounted it: