Try to use a thin tool like a razor blade to start to pry open the back cover.

When you opened it up just a little bit put a plastic card or a plastic opening tool inside the gap.

Using the plastic tool slowly make your way around the back cover. You can also use a guitar pick or similar.

Hint: the back cover is attached to the body with several plastic noses as well as a thin strip of adhesive. The cover is quite flexible and sturdy.