Cannot figure out how to remove door handle

Hi, I've got an old door handle and I can't seem to figure out the mechanics of how to remove it. I'm planning on replacing it with a locking handle. So far I've removed the two screws on the side, but the panel won't come off. I've looked all around the handle, and on the outer side only, there is a little metal slot that when pushed in with a screwdriver, allows one handle to come off. The other side has no such slot. However, when looking through the tube from the removed handle, I can see small metal tabs on the other side that look like they hold that handle on. I can't push them down though, with any tool I've tried. I'm not an expert, but I've replaced several door handles before, and this one has me completely stumped!!