You already have a minimum cost headlight. Putting higher wattage inside it won't give you much in terms of additional light.

If you want more light on the road, you have to spend the money to upgrade to the 3-code lamps.

They are about $200 for the pair. You can get them here:

http://www.importvision.com/index.php?display=show_part.php&PartMake=Mercedes&select_PartType=Headlights



If you can't spend the money, then leave them as is. Don't put larger bulbs in the existing lamps because the additional heat that you will generate will eventually give you some problems with the existing wiring.