I got really confused on this one and read lots of people breaking the VERY expensive clips.
Also found TIS to be not very helpful....to the point I dare say it's incorrect!!
How to remove the bumper corners:
The knack is to insert a plastic trim tool between the bumper and the black plastic thingy
This forces the bumper down towards the floor by a few mm and releases a few plastic tangs
You then need to pull the bumper out towards you. Not much force, it'll just pop out!
The black plastic thingy will stay attached to the wing.
I did both sides and didn't break the plastic thingies either
As this will probably be the last thing you do before the bumper is removed you'll need a small (2mm?) flat-blade screwdriver in your pocket to help detach the fog light connections, and a couple of hose clamps (Brake hose clamps?) to seal off the pipes going to the headlight washers so you don't lose all the washer fluid and drown.
Black plastic thingy:
Support, side panel front left
51117165179 or 7165179
Supersedes: 51117016065 or 7016065
Support, side panel front right
51117165180 or 7165180
Supersedes: 51117165180 or 7165180
Good luck
Kelvin