I used an allen key to push the inner part of the liner rivets through. a bit hard to move at first but just press hard..you have to press them fully through 'til they drop inside the bumper. then you can remove the outer part of the rivet, I just pulled the liner away from the bumper to free the outer part of the rivet. To refit rescue the inners from the bumper) push in the outer part of the rivet, and push the inner stem back into the middle of the rivet to expand it (all done from outside.)
The top front edge of the bumper just pulls outwards from the clip underneath,
Just pull it hard towards you, just as if you are pulling a wheel trim off a wheel and it will unclip. It takes a bit off effort but dont worry, you wont break it.
Push hard on it to refit and it will clip back in. simples....