To download macOS 10.14.13 —> which seems to be a maintenance upgrade —> go to the Settings app and click Software Update.
You can download iOS 12.1.3 by going to Settings —> General —> Software Update. It provides fixes for multiple bugs affecting iPad Pro, HomePod, CarPlay, and more.
You can install watchOS 5.1.3 by using the Watch app on your iPhone. It offers bug fixes and performance improvements.
You can update your Apple TV to the tvOS 12.1.2 update via the Settings menu on the Apple TV. It also offers bug fixes and performance improvements.