There will come a time when you'll want to reset your iPhone to a fresh-install of the opperating system. Follow these steps and you'll be good to go in about an hour or so. This will clear all personal data from the phone.
- Make sure your battery is fully charged before you start.
- From the home screen, open Settings.
- Tap on General.
- Scroll down and click Reset.
- Select Erase All Content and Settings.
- You'll be asked twice to confirm that you wish to erase everything.