If you are using the legs that came with it you will notice that on one end of the fixture you will see a line that divides two pieces of plastic. Basically the whole glass undercarrage will end up sliding over a bit and then you can get the legs started to slide down. It would have been nice if they had that in the instructions. I had to stare at it like a monkey doing a math problem for a while before I noticed the underpart would slide.
~Russ