Turn off your device and remove the SIM-card. Unscrew all of the ten screws on the back of the phone.
Don't worry about mixing up the screws as they are all identical. Even the 11th and final screw you'll be unscrewing is identical to the ones on the back cover.
The screw pointed out in the picture is covered by the warranty seal, which is a small black sticker. Remove the seal, and if you want, replace it when reassembling the phone.