This video will show you how to change the oil on a Mercedes Benz. The newer ones are a little different by the process is the same. Most places now have a place where you can drop off the old oil.
You will see that this is not very hard and it is a good place to start to learn how to work on your own car.
This is the same for 1984 to 1991.
380 SE
380 SEL
380 SEC
420 SEL
560 SEL
And other models.