... And gently but firmly remove the old headlight. Disconnect the power lead and the purple vacuum hose.
After removing the two headlights you have a rather naked looking SLK.
Installing the replacement headlights is a bit fiddly but basically it's the reverse of the above. First you'll find that a new 10mm bolt is installed. Fitting the lamp is easier of this is removed completely. Connect the purple vacuum hose and connect the car light connector to the headlamp harness (you'll need the adapter if you have a pre-facelift R170) then manoeuvre the headlight so it sits where it should and put the 10mm bolt in first but don't do it up tight. Fit the two 8mm bolts too and again, don't do them up tight.
The biggest issue I had was that the rubber seal wasn't well fastened to the headlamp and this needed 'persuading' into position.
Test the headlamp fitment by clearing away your tools and closing the bonnet (or hood). You can make final adjustments to the seal and the lamps then before tightening the lamps and click-fitting the indicators (which were quite hard to seat against the rubber seal. Be warned).
A final check that all the lights work (indicators / side lights / dipped and main beam) and then you can re-fit the grille. I must confess to gingerly closing the bonnet the first time....
One final check that everything works then it was off to my friendly MOT station to align the lights.
I think that's it. Next step is a little night driving to see how they behave and then a little think about the relay wiring. One small point I noticed is that the bulb failure lamp comes on when the main beam is lit. I understand this is expected, judging by other posts, but I'm sure we can fix this with a suitable resistor. I also need to work out where to fasten the relay to stop it flapping about as I drive.
Hope this helps someone. The whole exercise took about an hour. It would have been less if I'd not taken the photos!