There is a very good reason why Microsoft wants to force feed you the windows 10, and by installing the new operating system you will say the sweet goodbye for your privacy. Since this is a general topic on UE4 forums, and most of the users are very eager to play with the new OS (dx12 is a reason for example, worth it or not that is an another question) it is important to point out the consequences of such an upgrade. Great number of articles continously popping up to display the monstrosity and shady nature of the telemetry MS is conducting in large quantities, literally affecting >200 million windows users as of lately, who already unfortunate to be caught in the spin and have installed the biggest spyware ever made. While the desktop functionality is providing options to disable some of the mentioned behaviors, deeper analysis have pointed out it is still exchange known/unknown datas with remote services (including sensitive files, tracking informations, bits and pieces recorded from your microphone to analyse your voice characteristic and speech). The list of all these suspicios acts goes way beyond mentioned above, and i strongly suggest you to take your time, get a nice afternoon and google up this topic to make a well educated decision. It is very wise to do so.
As for the GWX (get windows x) you will continously get nagged and tricked to install the OS, fortunately it is nothing more but a dozen of windows 7/8 updates that you can uninstall to get rid of the pain. To do so, just start your searching for the word gwx and windows KB’s associated with it, that you can remove manually rather than using any third party remover tool (which is not prefered i assume).
While windows updates are well establised to be the corner stone of safe and secure computer operating, a few of these kb’s are seem to point out of this scope and may be safely removed without causing alarm.
And yet no one seems to mind that Apple and Google have been doing this with iOS and Android since the products were released. It’s only when Microsoft does something that people start sounding the trumps of doom.