In the UK we drive on the left side of the road, and our headlamps have a higher beam on the left side to further illuminate the kerbside. When we then go to a country which drives on the right, this higher beam will shine into the eyes of oncoming drivers, who are now on our left side.
I've recently taken a 2006 English Mercedes C220 CDI over to France and needed to change the dip to suit. The Mercedes handbook for the car wasn't helpful, suggesting it needed their workshop to do the trick.
These High Intensity Discharge (HID) lamps use a dangerously high voltage to strike the arc, so care must be taken. Ensure that the light switch is turned completely off, the ignition key removed, and that no-one else can switch on the lights while you have a hand in the housing ! Leave it all off until the housing has fully cooled before proceeding.
The rear of the lamp housing is covered by a plastic cover sealed with a soft O ring. Undoing the single clip will allow the cover to be removed. Access is a bit restricted, but with the aid of a small mirror you can see into the lamp housing. A couple of inches into the housing, on the outboard side, is a small white plastic (ceramic?) lever. This lever controls the dipping of the lamp. Avoid touching the lamp itself.
On the drivers side (right side as you face forward) the lever must be moved UP to set the dip for driving on the left, and DOWN for driving on the right.
On the passenger side the opposite is true.
The driving on the right setting, is also OK for driving on the left as the beam is then completely flat topped. But obviously you won't have quite such good visibility down the kerb line..
That's all.
Replace the cover, making sure the O ring is properly seated.
P.S. On my more recent (2012) Mercedes C180 the above is no longer necessary as the dip direction can be altered by software from the dashboard.