Steps to remove the battery.
The backplate is held down with internal clips, place a spudger inbetween the backplate and the midframe and py the backplate away from the device.
Once the clips are free, the backplate should be easily removed.
First remove the battery connector before you do anything else internally.
Gently lift under the battery cables to free the connector.
Remove the 6x screws holding the battery in place.