That's curious that, my last mot (June) the guy decided my headlights were too low, despite nothing changing over the last 6 years and he set about adjusting 'em, well it took him ages, I think he soon began regretting his gesture, backwards and forwards for various tools.
So I can't help with 'how' but I think it's not easy!
Afterwards I felt that they were too high and ran around with the 'in-car' adjustment set lower.