Replied to your other thread, but this forum is a better fit, so I will post again...
I was just playing around with this. There are two types of the mounts, the spring steel clamps, and bolt on. I have a broken bracket bolt on type, and a less than stellar looking spring clamp grille but with a good bracket.
first, you loosen the side bolt (it might be a screw, there are at least three variations):
then you stick a screw driver in from the front, on top of the tab, and then pull the grille off the bracket:
this is what the clamp looks like separated from the grille, the full width flat side is where you need to put the screw driver:
bottom of the tab of the grille:
top of the tab of the grille:
This is both types:
spring type bracket (and grille):
bolt on type bracket (and grille):