1. Remove the door card
2. Remove the C snapped clip that goes around the lock barrel
3. The central locking bracket that's attached should come away from the barrel
4. Push the barrel out of the door.
5. Fitting is the reverse, this is a little. It tricker trying to hold everything in place and get the C snapped clip back on, a helper holding the barrel in place on the other side of the door makes it much easier.
It's a tight squeeze working within the door with poor visibility but not hugely difficult.
Never tried it myself but there is a guide in the wiki. A good few others have done it before and again while it's a fidly task by all accounts not too dificult