There is nothing on the glass lid that suggests that you should be able to unscrew it, but it actually does.
When changing the bulbs on mine, I probably did the same mistake as you are doing. I first put a screwdriver between the bimini
and the 3mm thick light housing, but I couldn't get it out using reasonable force not to break things. Then I tried the unscrew the glass lid and it came off. I was a bit surprised as nothing suggested it would. I had to press real hard with all my fingers all around the edge of the glass lid to be able to do it.