To upgrade the iOS software on your iPhone, perform an update wirelessly through the Software Update option in the Settings section of the iPhone. Alternatively, connect your iPhone to a computer, and perform an update via iTunes.
Before upgrading the iOS software, create a backup via iTunes or iCloud in case the update corrupts the operating system. To perform an update through the iPhone, make sure that it’s connected to a wireless network and a power source. Tap on Settings, select the General option, and tap on Software Update. Tap on the Download and Install link, wait for the update to download, and tap Install once the prompt appears. If you’re using a passcode for your iPhone, you have to enter it before the update process initiates.
To upgrade the iOS software through iTunes, start the program, and plug in your iPhone to a computer on which iTunes is installed. Click on the iPhone icon in iTunes, open the Summary pane, and click on the Check for Updates button. If an update is available, select the Download and Update option. If an error reports that there isn’t enough storage space to perform an update, manually remove unneeded content on your iPhone. Once the update process completes, the iPhone should restore the amount of free space to its pre-update value.