Help removing ceiling return filter grille

[EasyRhino]

I have an air return with a filter that desperately needs replacement. Trouble is, I can't figure out how to remove/open the grille. It doesn't have the usual sliders, only two small metal tabs shown in the attached photo. They don't move when pushed or pulled, and there are no visible screws. There is a separate frame surrounding the grille, but again I don't see any mechanism for removing it.
Thanks for any ideas!

[Sergroum]

Has to be something related to the tabs. You don't seem to have a choices. Try skipping a screwdriver through and prying them backwards?