While holding the device with your non-dominant hand, use your dominant hand to gently pry the back casing off the device. The most effective way to do this is by gripping the small notch.
If it doesn't come off, try using alternative grips that are the most comfortable for you. Try using your fingernails to pry up at the corner or around the edge of the backing. The case should come off easily.
The back should be completely removed.