Removing & cleaning door lock.

As I can't insert the key in the door lock, I need to remove it & strip it down to see what the problem is. Nothing in "How To" so can somebody give advice on how to proceed
Also, the passenger door lock is blanked off & I would like to fit a new lock there.

Passenger blank is standard on remote central locking cars.

On removing lock.

Take off door card. Undo bolts in door edge holding door lock in place. Disconnect connecting levers.

The key barrel is held into the plastic door handle with a U shaped clip. If you're lucky the clip has been put in from underneath and you can slide it down and out. The barrel will now come out.
If you're unlucky the clip has been put in from the top and you'll need to remove the handle first(2 awkward hex headed screws)

The barrel is all held together with a C clip at the back. It will be jammed full of old polish and solidified grease.