Just looking at my bumper, it really might be easiest to remove the
complete bumper rather than try to take pieces off while on the car,
but it's your car and your time. Never done it, but from the manual on
CD:

Removal
1 Unscrew two nuts on rear center piece in trunk and two screws on rear
fender left and right.
2 Remove complete bumper toward the rear.

Disassembly
3 Unscrew nuts of protective rubber rail left and right from inside
bumber.
4 Pull off protective rubber rail.
5 Remove cover for bumper joint left and right.
6 Remove two screws each on joint of paneling under bumper.
7 Remove screws on paneling of bumper and remove paneling.
8 Remove screws on bumper shells and remove shells.
9 Disassemble reinforcment.

Assembly
10 For assembly proceed vice versa.

Installation
11 For installation proceed vice versa.  Watch out for rubber discs of
bumper holding bracket (body seal).