There are only 2 ways to update an iOS/iPadOS. Know how to...
Before any iOS / iPadOS update, please do the following
Go to Settings > General, and tap Profiles & Device Management. Tap the iOS Beta Software Profile. Tap Remove Profile, then restart your device --> How to uninstall iOS beta software - Apple Support
VPN or proxy connections might prevent your device from contacting the update servers.
If you still can't install the latest version of iOS, try downloading the update again:
- Go to Settings > General > [Device name] Storage.
- Find the iOS update in the list of apps.
- Tap the iOS update, then tap Delete Update.
- Go to Settings > General > Software Update and download the latest iOS update.
If you don’t see the update in the list of apps or if the issue happens again, you need to update your device with iTunes.
Try updating iOS after each step.
- Try to Forget the WiFi network and add it again
- Try another WiFi network
- Toggle sets automatically off and then on
- Reset your network settings
- Force restart your device
- Remove any beta profiles, if applicable