How do I tilt the cab on a Renault Midliner S130?

How do I tilt the cab of a Renault Midliner S130 7500Kg? There is a lever on the outside of the cab at the back but even when it's released, the cab won't tilt. There are no levers or controls inside the cab, and it seems to be a manual release mechanism; but no joy yet. Anybody got suggestions as to to how to do it, as I need to access to engine and box. I also need to change a headlight bulb and the fixings seem to be on the inside, so I can't get the front grill off to get at it. If I don't need to tilt the cab to do this, I can wait for further instructions later, but if anyone knows how to get to the rear of the headlight, that would be useful.
Thanks