I have never swapped a mercedes light however some things have applied to each I have changed.
Forget using a Haynes manual for the time being...
http://www.haynes.co.uk/webapp/wcs/...10001&storeId=10001&productId=15107&langId=-1
First call the dealer to see the part cost and the full job cost to get an idea of the time. If the time is high - its likely there needs to be housings removed.
There are three mounting points, one will be an unadjustible pivot and the other two will permit the light to be positioned. See how accessible these are.
Each will be a ball type fitting to permit its movement, and will have a cap/blade/spring clip to secure it in place. Unplugging the wiring generally helps to get better access.
Remove enough of the housings to get access to the fasteners keeping the ball/socket in place. Some have no fasteners and are just pushed in, but I would doubt mercedes would use this type.
When you can see how each faster works - figure if you have enough access to reattach it before you detach it. If in doubt remove more obstructions.
Each time you remove a part - tape the screw for each hole into the hole for each part you remove - so you know what goes where and dont finish the job with extra bits left over, or with a selection of screws that wont properly fit the hole left.
Presuming the light is broken already and you are not removing it to reseal etc. Its damaged already and you have nothing to lose if you are replacing it. But dont try to force things (other than spring clips) as you might find it was a false economy if you need to replace more than you planned.
One final thing - its always worthwhile going to a breakers yard that you know has a car like yours - as it gives you the chance to try the job on a car that is largely worthless already and very rarely are parts removed carefully in breakers yards, often just being cut out - so its not as if you are abusing their service.