It's pretty difficult if you don't have the equipment to extract the oil via the dipstick tube ... as is the design intent.
You'll have to remove some bottom paneling to get to the drain screw on the oil pan, and the liklihood of damaging this is significant.
As with anything German, washers used on drain plugs are NOT reusable.
Use only motor oil that meets Mercedes specification 229.5.
Changing the oil does not magically reset the "service needed" warning message. Find out how here
http://www.startekinfo.com