We’ll talk about a way to stop the notifications later. This method stops the automatic downloads, but unfortunately it won’t prevent macOS from bugging you unmercifully to make the update. Stop the Installer from Downloading Automatically Regardless of the reason, there are times where you don’t want to update and you might want to stop macOS from downloading the new version and stop getting those pesky notifications to upgrade.
Maybe you just don’t want your Mac to download a 5.21 GB installer program without you knowing, or you’d like to make a couple of backups before High Sierra is installed. Perhaps you’re not sure that macOS High Sierra is going to offer any improvement over Sierra or El Capitan, or you’ve heard about an issue that you’d like to avoid. Apple can be a bit insistent on trying to get your Mac updated to the latest version of macOS, but there are reasons why you may want to wait to perform a major upgrade - in the most recent case, your Mac wants you to update to macOS 10.13 High Sierra.