Usually, you have to remove the globe/diffusing glass first. You do this just like you would if you were going to replace the light bulbs. For the light fixture you have in your photo, you should be able to remove the globe/diffusing glass by simply twisting it until it come loose, as if your were unscrewing it. After the globe/diffusing glass has been removed, remove the light bulbs and place the globe and light bulbs out of the way.
The fixture should be held to the ceiling by either a rod in the center, or a pair of screws on either side of the fixture. Remove the rod or screws while carefully holding the fixture with one hand. Then, the fixture will come loose and be held up by just the electrical wires.
Use your wire cutters to cut the electrical wires, but be careful not to cut the house wiring. Only cut the fixture’s wires, including the ground wire. Then, the light fixture should be completely remove from the ceiling, and you can lay it aside.
Try to slightly twist the top and the bottom part. If that does not work, it might be held up by some strong adhesive. If that is the cause than you can just try to pull it out (not recommended). I would do more research or ask a possessional (maybe a house designer, preferably the one that helped build your house).
i have the same ceiling light yea the bottom part of it twist off be careful because if you drop it, it can shader or at least mine has ... x[ lolz