It may help to apply heat to the back cover using either a heat gun or an iOpener before starting to remove the cover.

Use a plastic opening pick to pry into the crease between the back cover and the midframe of the phone.

Move all the way around the phone until the back cover is separated from the rest of the phone.

The images show a metal spudger being used to pry open the back cover. However, this process is not recommended, as it poses a puncture risk to the battery.