The lower center grill is removed from the back and requires
removal of the bumper.
Not sure about the outer grills, but I think they are the same.
The lower center grill is held in by numerous plastic clips
that need to to be released to free the grill.
There are notches in the bumper that engage plastic clips on the perimeter of the grill.
If I recall correctly, there are a total of 18 - 6 across the bottom,
8 across the top and 2 on each side.
Once you
remove the bumper it will be clear.
backside view of lower grill removed
close up of two of the clips