First of all Win 10 has only been out for less then a year, not 2-3
Copy this to a notepad document and save it as DissableAutoUpdate.reg
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\GWX]
"DisableGWX"=dword:00000001
[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate]
"DisableOSUpgrade"=dword:00000001
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate\OSUpgrade]
"AllowOSUpgrade"=dword:00000000
"ReservationsAllowed"=dword:00000000
If you are not on the computer in question then save the file to a flash disk or other media.
Now reschedule the upgrade to tomorrow.
Then move thie .reg file you created to the desktop and run it
Unfortunately MS has switched from a nag-screen to auto-schedule.
Win 10 is a good OS, but you have to disable all the advertisement crap (which is why MS is giving it away for free and pushing it on everyone).