Usually, clicking on the Red X located in the upper right corner means the user wishes to “Cancel” a pending action as has been the norm for ages.
Closing the GWX pop up by clicking on the Red Xper Microsoft “If you click on OK or on the red “X”, you’re all set for the upgrade and there is nothing further to do.”
If you read the fine print as shown below you need to either “change the upgrade schedule or cancel scheduled upgrade” by clicking on the word “here”.
This takes you to the next window where to cancel the upgrade you need to click on “Cancel scheduled upgrade” link.
Now you will finally see in the next window the option to “Cancel scheduled upgrade”, click on this button to cancel the upgrade.
To be certain this stopped the upgrade to Windows 10 from taking place, you need to open Windows Update manually as follows.
1) Click ‘Start’, right click on ‘Control Panel’, in the upper right corner select: View by ‘Small icons’. 2) Click on the ‘Windows Update’ icon (last icon in the Control Panel list) to open Windows Update. Warning: Do not start the update (Don’t click on the ‘Get started’ button).
If you see (as shown below) the following “Upgrade to Windows 10” then you need to click on the “Show all available updates” link.
Locate the “Upgrade to Windows 10...” Entry, remove the check mark from the box (Single click). Next hide this update by right clicking and choose the hide update option.
Now whatever you do, stay away / resist the urge to click on the GWX icon or you may need to go through the whole process again to stop the update.