I took mine off at the weekend to steam clean the engine bay/intercooler etc as i have a slow oil leak and it was caked!!
The bumper is held on with 4 panel fairings (metal spring like clips with m10 bolts) to the wings - these are only accessible through the arches (its a PITA to try and get to them by removing the headlights). The splitter/black trim under the bumper is help on with 6 or 8 of these fairings as well.
You'll need to undo the arch liners to access the bumper fairings on either side - I found it easier to take both front wheels off for access. Theres some pop-pins holding the arch liners on and 4 philips screws at the back (one is underneath) which are easier to prise off without the wheels there (especially to get a spanner in too!) - it'll also make adjusting the bumper easier - there isn't a lot of adjustability although I imagine using correct fittings would be a start...