I have had this request from people that don't want to upgrade to Windows 10,
but get constantly bugged by the Windows 10 Upgrade Notifications.
So here is a way to stop it:
The most common Windows 10 update notifications you will see will open in the middle of the screen every time you start the computer and occasionally pop up in the bottom right corner. These can be closed, but you will still have an icon on your taskbar that cannot be removed.
These endless pop ups started showing up after Windows 10 was released because of an update (KB3035583) pushed out by Microsoft for Windows 7, 8 and 8.1. This is listed as a "recommended" update in the Windows Updates manager, but it is an executable program that runs when the PC boots and constantly reminds you that you can upgrade to Windows 10 for free. It doesn't do anything else, so it can be removed without jeopardizing the safety, stability or security of your PC.
To do this, open Control Panel and choose "Uninstall a Program." Then on the left side, click "View Installed Updates" and scroll down until you find KB3035583 and uninstall it. Once it is gone, you won't get these notifications anymore.
As it is a recommended Windows update, Windows will try to install it again, so be sure to go into the Windows Update manager, right click on KB3035583, and select "Hide Update".