Take your time!

Use a guitar pick, although some have successfully used a fingernail. Don't use a screwdriver as you will damage the case.

Start at one corner and carefully insert your tool, working it along the seam until you hear a click and the case starts to come apart.

Carry on working your way around the case. Be very careful near the buttons.

Eventually the rear case will come away. There aren't any wires attached to the rear case, it just lifts off.

When it's time to reassemble, clip the rear cover back on carefully, making sure to fit the side with the buttons first and being careful to ensure they are positioned correctly.