Have you figured out how to do it yet? I think it depends on the maufacturer and/or model...and how old the fixture is. I have some with reflectors that are held in place by a couple screws. I'm really not sure, but it seems that with some of them, you have to remove the end pieces that the tubes mount into. You might pop into a hardware store and ask someone in the lighting department.

Thanks, I did. I just needed to press in on the sides to push back a little blister in the metal, a little, that holds on the cover. There are even little blisters in the sides above where the ones that hold the cover to indicate where to squeeze so I feel dumb.