I was going to install a zwave GE switch in one of our room and found out that it wouldn’t fit inside due to two tabs on the side that I believe is for the mechanism that holds the switch box snug against the drywall. I’m thinking of replacing it with the regular plastic box that has a little bit more room for me to stuff the wires and the switch.
My question… how does this old switch box work?? Just loosen the screw and it would disengage from the drywall?
Replacing with this one…
I’m not qualified to discuss switching out the switchbox, but if you read the directions that came with the GE switch, I think you’ll find that they tell you that the two tabs can be broken off if you need more room in the switchbox. This information will probably be in a section that discusses double gang or triple gang boxes. But make sure that that does apply to your model before doing anything, of course. 
edited to add sorry, I misunderstood. I thought you meant two tabs sticking out of the zwave switch, not the two metal pieces that are part of the box install.
Also, typically the tabs attached means its capable of handling a higher wattage. Breaking off the tabs could reduce the supported wattage, FYI.
It’s actually the inside assembly (body) of the GE switch that will not slide in the switch box. The picture above is the closest one I could find.
If it was installed with your house it’s a “new construction” installation which means it has a huge nail going deep into the stud adjacent. I hate to get a fine toothed hacksaw which killed the blade and my shoulder but it worked. There should only be one or two nails. Good luck!
This room as an add-on. I circled the tabs that I believe is holding the box to the drywall. I loosened the left one but didn’t touch the right screws. The two inside strips of metal are preventing me from sliding the GE switch into the box.
My experience is pretty exclusive to plastic boxes. If I were to guess those screws are something like @pstuart mentioned. Have you pulled all of the wiring out yet to see if there’s any screws in the back? (Power turned off of course.)
Both of your photos are of retrofit boxes, designed for existing construction when the boxes can not be affixed to a stud. The metal one has ears that move along a screw, and the newer plastic one has tabs that hinge out, and then move in to clamp on the dry wall.
As for removing the old box, just loosen the screws the little ears ride on until there is enough slop so you can push the box back into the hole so you can rotate it so the short dimension of the box is aligned with the long dimension of the cutout, allowing you to remove it.
Glad someone has seen one of these.
Thanks! I will tackle this on the weekend. I was going to give up and return the switch but I couldn’t bring myself to do that