The two control knobs screw off (normal thread). Just secure the part inside the camera so it won't turn (i.e. stick a screwdriver in it) and unscrew the screws on top of the knobs. When these are removed, a couple screws will be revealed (one near the edge of each end under where the knobs were). These screws are what hold the top on. Unscrew them and the top comes off. You'll want to keep an eye on a few little parts which will probably fall out (viewfinder lens and cover).
Getting the top back ON:
Pretty much the reverse of the above. The only tricky part is getting the frame counter in position. The problem is pretty obvious when you look at it. It's also pretty simple to jiggle it into position to get the top on. Frame counter note: If you decide you want to remove the frame counter for some reason, it has backwards screw threads (i.e. turn clockwise to loosen). Several folks (including myself) snapped off the screw before learning this lesson.