With the information i have, I'd guess your monitor is held together by clips between the bezel and back. Taking apart your monitor WILL void your warranty - and its not easy to do cleanly without practice. With the BenQ monitors i've taken apart in the past, there was an obvious slot to take it apart in the middle bottom of the frame.Make sure that there's no screws, especially under labels - if there are any undo them.
When i did it, i used a small flathead screwdriver, and a set of sharpened dowels (acting as wedges to keep the pryed apart parts apart). Start at one point, pry, and wedge, and work your way around the edge of the area between the bezel and back of the case. If it won't come apart, check for non obvious screws. You may prefer to use a set of spudgers (ifixit and others have them) - they are pretty cheap and probably worth it if you wanted to avoid cosmetic damage.