Is your device compatible to update to the new version? See the article(s) below.
IOS 15 and iPadOS 15 Compatible Devices. *
iOS 14 and iPadOS 14 Compatible Devices. *
See the articles below.
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 or later to do the update?
Update software on iOS devices in iTunes on Mac. -
Phone, iPad, or iPod touch - Update with Finder. *
iPhone, iPad, or iPod touch - Update with iTunes. *
If you see an error when you update or restore your iPhone, iPad, or iPod *
Updating iOS: common issues and solutions. -