Remove the back cover using a plastic opening tool. Insert it into each corner starting at the upper left of the back cover and pushing out.
You may also use your finger nail if you do not have a plastic opening tool at hand.
Using a plastic opening tool, push out the battery by inserting it into the small groove at the top left corner of the battery and pushing out.
The battery snaps out of place and you can remove it using your fingers.
When you are ready to insert a battery make sure the three copper teeth on the phone are aligned with the 3 copper dents on the battery.