It’s even easier than you think.
After you tap “Install Now” and it finishes successfully, a page will pop up letting you know the update was successful. You will also receive a notification as well once it was successfully installed.
If you’re updating manually, you’ll just need to reboot your device to complete the process—and the restart button will be right there on the screen to make it easy.
You can also go to Settings, tap System, then System Updates. From there, tap the refresh button in the top right corner, and if the screen says “Up to date”, you’re all set—the update went through successfully.
Quick check, clear answer, no guessing.