Setting up iPhone

You might be unable to update your iPhone for one of these reasons. 

• Not enough available storage space on your device 
• Downloading the update takes a long time 
• Unable to reach the update server 
• The update doesn't complete 

Hope these Apple Support links can solve your issue. 

• If you can't update or restore your iPhone, iPad, or iPod touch 
• Get help with over-the-air iOS updates 

Hope it helps! 

If you still can't install the latest version of iOS, try downloading the update again:

1. Go to Settings > General > [Device name] Storage.
2. Find the iOS update in the list of apps.
3. Tap the iOS update, then tap Delete Update.
4. 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 Forget the WiFi network and add again
• Try another WiFi network 
• Toggle set automatically off and then on
• Reset your network settings
• Force restart your device
• Remove any beta profiles, if applicable
• If everything fails:- Use iTunes or Finder (for macOS Catalina+) to update your device instead of over-the-air

• Get help with iOS update and restore errors - Apple Support
• If you see an error when you update or restore your iPhone, iPad