You can use iTunes to update or reinstall iPhone software, restore default settings, and delete all data on iPhone.
If you update, the iPhone software is updated. Your downloaded applications, settings, and data aren’t affected.
NOTE: In some cases, an update may also include restoring iPhone.
If you restore, the latest version of iPhone software is reinstalled, settings are restored to their defaults, and data stored on iPhone is deleted, including downloaded applications, songs, videos, contacts, photos, calendar information, and any other data. If you’ve backed up iPhone with iTunes on your computer, you can restore data from the backup at the end of the restore process.
Deleted data is no longer accessible via the iPhone user interface, but isn’t erased from your iPhone. For information about erasing all content and settings, see Resetting iPhone.
Make sure you have an Internet connection and have installed the latest version of iTunes from www.apple.com/itunes.
Connect iPhone to your computer.
Select iPhone in the iTunes sidebar and click the Summary tab.
Click “Check for Update.” iTunes tells you if there’s a newer version of the iPhone software available.
Click Update to install the latest version of the software. Or click Restore to restore. Follow the onscreen instructions to complete the restore process.
For more information about updating and restoring iPhone software, go to www.apple.com/support and search for HT1414.