There are 3 self tapping bolts with a 8mm (I think) sized hex head on the under side of the actual bumper. 1 attaching the bumper to the trailing edge of each arch and 1 just beside the exhaust recess, on the offside of the exhaust!
use a 17mm socket on the 4 bolts underneath (2 either side) you may have to move the exhaust for 2 of them!
Once these are all undone you slide the bumper off.
In true Haynes style refitting is the reversal of removal. But you may need to fish around to get the holes to line up.