as for removing the door panel, take a look at this site...i recommend to disconnect the battery because there is an airbag in the door, just for a safety precaution
E46 Fanatics: 3-Series, BMW Forums, BMW Modifications, E46 BMW
after the door panel is removed, carefully peel back the foam lining inside the door panel. next remove the screws holding in the lock actuator, its pretty self explanitory, just remember to pay attention to how everything is installed and hooked up, take pictures if you need to, then just reinstall everything in the same order it came out