Make sure you're connected to Wi-Fi . To do so, swipe down from the top left of your iPhone's screen and look for the Wi-Fi icon; tap it to enable Wi-Fi before continuing.
Open your iPhone's Settings . It's a grey app with a gear on it. The app icon may look different if you are using a different theme for your iPhone.
Scroll down and tap General
Tap Software Update.It’s at the top of the menu.
Tap Download and Install or Install Now . If a software update is already downloaded, the Install Now button will appear below the update description.
Enter your passcode if prompted. Enter the passcode you use to unlock your phone.