Recently I selected update all from the Mac Store which downloaded the latest version of OS X High Sierra. This is not an update I want or need at this time, issues abound which is enough said.
I found it tricky to remove the update from the list on the Appstore. It turns out there is a slight bug on the App Store app whereby Right Clicking in the description doesn’t always register. To reveal the hide this update it is sometime necessary to click in-between the characters, you may need to right click about a little to bring up the button.
To remove this update if you chose it mistakenly you first need to remove the downloaded package from you Application folder then right click (control click) on the description in the App Store listing and when it appears chose hide this update.
Apple in their wisdom seem to delight in us having to jump through hoops at the simplest of tasks.