Have you got the intelligent light system? If so there is a sub menu under "settings-lights-left or right" on your steering wheel buttons.
If not then it is a manual switch in headlights job.
Rear of headlights, black plastic cover,turn anti clock to remove,inside is a little lever which you push down to alter beam, there are lots of threads about it.
Two things,Make sure lights and ignition is off, second you will need the luck of the devil, a mirror and torch plus fingers on universal joints to find the lever and operate it. I've seen grown men tear their own heads off in frustration trying to do this. Some people say they had a friend who knew a man who had done it but I don't believe them.
I opted for the intelligent light option to save losing any more skin and life expectancy when i replaced my 211. Not cheap but how expensive is a rage induced heart attack?