You need to start the engine, let it run a bit, then shut & down and check the level after 5-10 minutes. I believe the spec for your car is something like 6.9 quarts but I'd have to double-check. It is definitely more than 6 quarts! And Mercedes specifically states you should NOT drain the oil cooler. The system is designed to leave the old oil in the cooler & hoses during changes - this is normal. The filter holds about a quart, which is why you're seeing "overfull" right now. Don't forget to check on a level surface, too!
Note - you'll get a LOT more response to 240D questions over on the Diesel forum!