Pull up on the exposed clear plastic tab to peel the battery off the adhesive securing it to the iPhone.

If the tab breaks before the battery is freed, apply a few drops of high concentration (over 90%) isopropyl alcohol under the edge of the battery. Wait about one minute for the alcohol solution to weaken the adhesive. Carefully slide a spudger under the battery tab to release the adhesive.

Prying in other places may cause damage. Don't try to forcefully lever the battery out. If needed, apply a few more drops of alcohol to further weaken the adhesive. Never deform or puncture the battery with your pry tool.

If there's any alcohol solution remaining in the phone, carefully wipe it off or allow it to air dry before installing your new battery.

Remove the battery.

If your replacement battery came in a plastic sleeve, remove it before installation by pulling it away from the the ribbon cable.

Before reassembly, clean metal-to-metal contact points with a de-greaser such as windex. The oils from your fingers have the potential to cause wireless interference issues.

Perform a hard reset after reassembly. This can prevent several issues and simplify troubleshooting.