How to change drivers door latch on vw golf sdi 1999 as drivers door opens when driving

Have you tried using WD-40 to help the lock from sticking you may not need replace it.
However if you feel it's necessary ...you need to remove the inside door panel with the window up remove the two bars that are you inner lock and door handle levers a plastic clip holds them into place on the lock itself .a drop light is very helpful once the levers are disconnected remove the outer screws on the door itself the lock should fall off from the inside at this point ...install new lock and reinstall rods { levers} to the lock itself test before reinstalling door panel then secure when confident it works properly