Find the left side of the ZEN. You can see in the picture that I learned by trial & error how to open my ZEN. If you do it right, you won't leave those gouge marks on the case.

The red rectangles indicate where the tabs are inside the case. They are 0.5" in from the outer edge.

Insert one thin screwdriver in the seam of the case right over the tab (red rectangles, remember?). Pry upward (gently!), forcing the lower half of the shell to flex outward. See pics 2 & 3.