Pull it up against a wall and turn the lights on.
set the internal switch to its highest setting and make a mark on the wall where both lights shine (the top of the lights)
Drop the switch to it's lowest setting...
then on top on the lights (under the bonnet) there should be a white bit of plastic with what looks like a phillips head screw on it. turn these and the lights shoudl rise/fall.
put both lights up a bit and line them up with the marks on the wall. i.e. where the highest setting was. then go to the car and raise them back up again!
this is if I remember correctly from when i did mine.
the MOT checker will not allow the lights to be too high though which is why when I go to have my MOT done I lower the lights using the internal switch to the reccomended level
Darren