The procedure has been modified to be more comprehensible and include instructions for both Windows 7 and Windows 8.1.
In Windows 7, click on the Start Menu, enter Task Scheduler then click on it;
In Windows 8.1 press on the Win key + S (or Win key + C keys and click on Search) keys to open the Search
interface, enter Task Scheduler and click on it;
Navigate to the following folder in the left pane: Task Scheduler Library\Microsoft\Windows\Setup\gwx (you can list the content of the folders by clicking on the little arrow on their left);
From there, right-click on each of the task below and select Disable;
Close the Task Scheduler and restart your computer;
To re-enable it, simply right-click on these tasks and select Enable instead.
OR in command line execute:
taskkill /f /im GWX.exe
taskkill /f /im GWXUX.exe