Follow each step carefully.
Press and hold the side button and the volume down button simultaneously until the power off slider appears. Slide to power off.
Use a P2 pentalobe screwdriver to remove the two screws located next to the lightning port.
Insert a plastic opening tool into the gap between the screen and the rear case. Gently pry open the device.
Use a spudger to carefully disconnect the battery connector from the logic board.
Use a battery adhesive remover to lift the battery out of its compartment.
Place the new battery into the compartment and reconnect the battery connector to the logic board.
Align the screen with the rear case and press down gently until it clicks into place.
Use the P2 pentalobe screwdriver to reinsert the two screws next to the lightning port.
Press and hold the side button until the Apple logo appears.