I want to update my iPhone 7 to the latest iOS update

The "latest" update for the iPhone 7 is iOS 15.8.3

You likely already have this, but tap Settings > General > Software Update to confirm.

The iPhone 7 cannot update to iOS 16 or iOS 17, if that might really be what you are asking here.

Unfortunately, the iPhone 7 is not compatible with the latest version of iOS - iOS 17.

To see the full compatibility list, see here: iPhone models compatible with iOS 17