If you want to get your battery replaced it can cost anywhere from £40-100 for your beloved iphone. Mine has been dying for a while and barely holds any charge so I thought I'd try this kit.
It comes with everything you need. Simply loosen the screws at the bottom with the provided screw driver, then use the tool to carefully pop off the front screen, be careful not to open it beyond 9 degrees at this point because you need to disconnect the screen cables before you can take it off completely.
Once those are disconnected unscrew the piece near the battery, and pull out the sticky tabs from under the battery, reove the old one and replace the new one, and put it back together.
There are some comprehensive videos on youtube and its far simpler to do than it sounds, and is a very cheap way of renewing your iphone when it becomes essentially useless from the dead battery. Very good kit.