Remove the battery.
Use a spudger to scrape away any remaining adhesive from the phone, and clean the glued areas with isopropyl alcohol and a lint-free cloth.
Secure the new battery with pre-cut adhesive or double-sided adhesive tape. In order to position it correctly, apply the new adhesive into the phone, not directly onto the battery. The adhesive should not touch any of the cables under the battery.
Press the battery firmly into place for 20-30 seconds.