First do what is probably the intended thing: hold the glass firmly near the ends between thumb and fingers on both sides, use rubber gloves if it helps, and try hard to pull it off. The metal clips holding it to the bulb socket should pop off. Try rocking it side to side. If that doesn't work ...
Use a screwdriver in one of the two noted locations (green), or both, or the similar one on the opposite side, should help to dislodge the horseshoe-shaped bracket (yellow) from the bulb socket. The glass cover and the two brackets should come off together.
If THAT doesn't work,loosen the nut holding the bulb socket on (right side of the photo). This will allow you to jiggle the socket, which may loosen the grip of the horseshoe bracket. You'll have to feel your way to being both forceful and non-destructive. And you may fail.
If even that doesn't work, this is desperate but use a screwdriver in the red location to bend the little metal flap up. This may destroy the bracket or the glass. It's a step to try before throwing the whole thing away.
