http://www.pcmag.com/news/343272/never10-tool-stops-accidental-windows-10-upgrades
"Gibson's new tool, dubbed "Never10," is a simple utility that runs on Windows 7 or 8.1 and disables Windows from automatically upgrading to Microsoft's latest operating system.
"The name 'Never 10' is a bit of an overstatement, since this utility may also be used to easily re-enable Windows operating system automatic upgrading," Gibson said in a statement. "But the primary reason for using this is to disable Windows' pestering insistence upon upgrading Windows 7 or 8.1 to Windows 10."
From above tool link:
"The elegance of this “Never 10” utility, is that it does not
install ANY software of its own. It simply and quickly
performs the required system editing for its user."