- Go to the menus Settings-> General-> Software Update.
- If a notification appears indicating that an update is available, hit the Download and Install option to proceed.
- Tap Install to update the program right now. If you don't want to wait, hit Later and then Install Tonight or Remind Me Later.
If you want to Install Tonight, make sure your iPhone is plugged in and has enough power to complete the update. The update will be applied to your device automatically over the course of the night.