The Apple iOS 12 operating system will automatically update the operating system for iPhone and iPad. The App Store can also automatically update your installed apps. Here’s how to enable these updates, or disable them if you want to update manually.
For example, you can turn off automatic updating of the operating system and applications to save data.
Operating system updates
To turn automatic operating system updates on or off, go to Settings > General > Software Update.
Here you will see if automatic updates are enabled. If you don’t see this option, you haven’t installed iOS 12 yet.
To turn updates on or off, click Automatic Updates and set the slider to On or Off.