Use iTunes to update. Update your iPhone, iPad, or iPod touch - Apple Support
Update your device using your computer
If you can’t update wirelessly on your device, you can update manually using a computer that you trust. If your computer is using Personal Hotspot on the device that you’re updating, connect your computer to a different Wi-Fi or Ethernet network before you update.
- On a Mac with macOS Catalina 10.15, open Finder. On a Mac with macOS Mojave 10.14 or earlier, or on a PC, open iTunes.
- Connect your device to your computer.
- Locate your device on your computer.
- Click General or Settings, then click Check for Update.
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Click Download and Update.
If asked, enter your passcode. If you don't know your passcode, learn what to do.