Few tools are required to do this.
A small plastic pry tool or even a fingernail is sufficient. Working area surface should be clean and dry with adequate lighting.
Immediately wash hands after handling the battery and completing the process. Discard the dead battery properly.
Pry off the back and separate it from the front of the phone case. You will see the battery once the cover is removed.
On both sides of the battery, there is a lighter grey half-circle. This is the best place to use your fingers to gently lift the battery free of the housing. Set aside the old battery, then replace it with the new battery. It should easily fit into place.
Replace backing of phone, pressing gently to secure to back of phone case