Removing the battery is an essential step in opening up the phone.
First, flip the phone over so that the back is facing you.
Next, using both thumbs, carefully push the back side of the phone's exterior up, removing it from the main section of the phone.
Set this piece aside until you need to reassemble the phone.
Insert thumb and pointer finger into the notch above the battery. Pull the battery away from the rest of the phone and set it aside.