how to replace the driver side door cylinder key switch ,in 2006 Buick lacrosse

You have to take the door panel off. Then you can access the lock assembly.

thank you! , my problem is that the key won't turn, and the dealer wants over $275.00 for install a new door cylinder ,plus labor, I was wondering to bring the car to a good locks smith to do it what do you think of it. Kindest Regards, .nuvista11

It won't turn because nobody uses a key anymore. They use the remote key fobs instead. Spray P.B. Blaster or WD 40 into the lock opening with the red hose. Put the key in and out repeatedly. It may take a few days of spray and key in and out while trying to turn the key. Then it should at some point start turning like it's supposed to. I've fixed A LOT of locks that way.