Ensure the latest version of iTunes is installed on the computer. The latest version may be installed from the iTunes website (http://www.apple.com/itunes/).
Connect the iPhone to a computer using the supplied USB cable.
Open the iTunes application on the computer, then click iPhone.
Note: If the sidebar is displayed, click the iPhone name under DEVICES.
Click Update or Check for Update.
If prompted that the iPhone software is up to date, click OK, and then unplug the handset from the computer.
If an update is available, click Download and Update and follow the prompts to install the update.
The iPhone software is now updated.