For update or restore iPhone software you have to use iTunes. You should always update iPhone to use the latest software. You can also restore the software, which returns iPhone to its original state.

Warning: all data will be erased from iPhone  All iPhone settings are restored to their original state.

1. Installing the latest version of iTunes from www.apple.com/itunes.
2. Connect iPhone to your computer.
3. In iTunes, select iPhone in the Source pane and click the Summary tab. Continue Reading »
Updating and Restoring iPhone Software