Pull the back plate up by gently twisting slightly towards the top left corner. When you feel the catch release, you can fold the plate back like a book cover.

Be careful of the connectors. There are two very small wires which run to the back cover of the phone.

If you accidentally pull the wires out, don't panic. The connector can be pushed back into place very easily.

If you are confident in your ability to reassemble the device, pulling the connector out can make this process easier by getting the back casing out of the way.