How do you change motor oil in C5?

remove a plastic cover from the bottom of car, than you can see a screw (key 21) or imbus 10. turn off a screw and let oil to go out in some balloon. remove a cup from motor, to remove vacuum and make oil go faster. when is out (about 10 minutes), remove oil filter. put a new filter, back a screw, and fill a new oil (total quartz 7000 about 4.0 liter) that's it!