Buick LaCrosse Owner's Manual page 446

Use the floor mat with the
correct side up. Do not turn
it over.
Do not place anything on top of
the driver side floor mat.
Use only a single floor mat on
the driver side.
Do not place one floor mat on
top of another.
Pull up on the rear of the floor mat
to unlock each retainer and remove.
Reinstall by lining up the floor mat
retainer openings over the carpet
retainers and snap into position.
Make sure the floor mat is properly
secured in place.
Verify the floor mat does not
interfere with the pedals.