Here is an Oil Change DIY for a 2001-2007 Mercedes C-Class (W203).

Works For:
2001 Mercedes C-Class
2002 Mercedes C-Class
2003 Mercedes C-Class
2004 Mercedes C-Class
2005 Mercedes C-Class
2006 Mercedes C-Class
2007 Mercedes C-Class

Source: BenzWorld

This only applies to 2001-2005 (I-4 supercharged engines) or w203 chasis. It might be the similar for other C-class models.

Tools Needed:
1. 27 mm socket or a cresent wrench
2. Small flat head screwdriver
3. Funnel
4. 8mm socket *
5. 1/2 inch socket *
6. Lift Jack*
7. Oil collection pan*

* Optional tools, only needed if you plan to drain the oil. If you suck the oil out these tools are not needed.

Parts/Supplies Needed:
1. Oil Filter (MB Part # A 271 180 00 09). My dealer provided a new drain plug washer the filter.
2. Oil (Mobile One 0-40) C230 (I4 SC) needs 5.8-6.0 quarts.

Procedure:
1. Locate the oil filter and slightly loosen it, DO NOT remove it at this time. This will allow the oil in the filter to flow back to the oil pan. (See Photos 1 &2 below)
2. Jack up the car and remove plastic engine covers on the bottom of the car with 8mm socket.**
3. Located oil pan drain plug and remove plug with 1/2″ socket (See Photo 3 below) Make sure you have the oil collection pan under drain, because the oil will come flowing out fast.**
4. As the oil is draining out, remove the oil filter from engine bay.
5. Remove oil filter cartridge (this may take a little force) and three rubber o-rings. Replace oil filter cartridge and replace the three o-rings (See Photo 4 below) Coat the new o-rings with some new oil.
6. Install drain plug with new washer and tighten to the proper torque spec (24N/m) or 1/2 turn past finger tight.
7. Install oil filter into engine bay. DO NOT over tighten! Tight to the proper torque spec (24 N/m) or if you do NOT have a torque wrench tight a 1/4 turn past hand tight.
8. Remove oil cap and input 5.25 quarts of oil using the funnel. (The reason why you should NOT add the entire 5.8 quarts is because there is still some residual oil in the engine and it’s not good to over fill. You can easly add oil, pain to take it out)
9. After putting in 5.25 qts, turn ignition key to position 2 (radio and heater/AC comes on) for 10 seconds. This will allow the oil pump to start pumping the oil into the empty filter. Then start the engine and let it run for one minute and turn off car and remove key.
10. Re-Intsall plastic engine covers on the bottom of the car with 8mm socket and lower jack(s). **

** Steps not needed if user decides to suck the engine oil out using an oil extractor (topsider or etc.). To suck the oil out simpley put suction tube in oil output hole (see photos 1 below) and make sure tube goes all the way to the bottom.

Check Engine Oil: (See Details More In Drivers Manual)
1. Be Parked on level ground and have car stationary for at least 5 minutes.
2. Turn key to postion 2 (radio and heater/AC fan turn on).
3. Change to standard display (mileage) on the multifuction display (computer display under speedometer).
4. Press and hold ^ or V on steering wheel for 3 seconds until “ENGINE OIL LEVEL – MEASUREMENT IN PROGESS! CORRECT MEASUREMENT ONLY IN VEH. LEVEL” will appear. After 3 seconds “ENGINE OIL LEVEL – MEASUREMENT NOW” will display.
5. Computer will return the following message:
> ENGINE OIL LEVEL – OK
> ENGINE OIL LEVEL – ADD 1.0 QUART (1.0 LITER)!
> ENGINE OIL LEVEL – ADD 1.5 QUART (2.0 LITER)!
> ENGINE OIL LEVEL – REDUCE OIL LEVEL
> ENGINE OIL LEVEL – OK
6. Add oil if needed.
7. If you get “OBSERVE WAITING PERIOD” then remove key from dash and wait 5 min. If you get “MEASURING NOT POSSIBLE” then repeat steps above.

IF YOU CANNOT VIEW PHOTOS THEN USE THIS LINK: http://www.brianrichardson.net/c230/c230_oilchange.ppt

I recommend rotating tires after every oil change.
Good Luck & have fun!