Upgrade to iPhone to iOS 14

• If you have an iPhone 5S or 6/6plus, the highest you can update to is 12.5.6

• If you have an iPhone 6S through 7, you can update to 15.7

• If you have an iPhone 8 or higher, you can update to 16.0.2

Go to Settings > General > Software Update.

Update your iPhone, iPad, or iPod touch using WiFi -

Update your iPhone or iPad - Apple Support

Update using your computer -

Update iOS on iPhone - Apple Support

If you have an iPhone 14 it is capable of running iOS 16.

iOS 14 is not available anymore through apple, every iPhone that can run iOS 14 can run iOS 15. So update to iOS 15.7 instead.

If you have an phone that is now on iOS 12.5.6, you cannot update further due to hardware limiatations

On what iPhone model? What iOS version is currently running on it?