HOW MANY MILES ACTUALY I HAVE TO CHANGES OIL THE CAR

ever 3000 miles or 3 months which ever comes first

Mercedes are particular abut the oil they want used in that engine. They require "European spec" synthetic oil, and insist traditional oil not be used. I would change it every 5 or 6,000 miles.

If you want a more effective maintenance I recommend changing the oil and filter every 2K on petroleum and 4k on synthetic. Why wait till the oil and filter expires changing it before and will result in longer engine life. Don't all ways believe the manufacture, use commonsense