I want to update my iOS from 15 to 16

Hello,

There are different ways to ensure the highest iOS that your device will support is installed on your device.

This support article has instructions about updating an iPhone or iPad wirelessly --> Update your iPhone or iPad - Apple Support

You can also use Mac and PC computers to update system software: Update iOS on iPhone - Apple Support

With an iPhone 8 or higher, you can currently update to the latest iOS 16.3.1