Why my iPhone is not updating?

See if anything here helps.

Update your iOS device.        

Get help with over-the-air iOS updates          

Update – Can’t or can’t restore 

Have you tried using iTunes on a computer or Finder if running Catalina to do the update?

 Update software on iOS devices in iTunes on Mac

If you see an error when you update or restore your iPhone, iPad, or iPod      

What happens when you attempt to update?

What is the existing version of iOS?

Which model of iPhone?