How to update iPhone to iOS 12?
How to update iOS 12
[Re-Titled by Moderator]
Depends. If your iPhone is an 6s or newer, you can't. From that model on, you can only update to the latest iOS version, there is no picking & choosing. If it is from 5s to 6, you can update up to iOS 12.5.5. If it is older, can only update up to iOS 10.3.3.
Edit: iOS 16 can only be installed in iPhone 8 or newer. From 6s to 7, can only go up to iOS 15.7.