It would be nice if Microsoft allowed a "No thank you" option to it's Windows 10 upgrade prompts, but to date they have not. They want as many Windows 7 and 8 users to upgrade as quickly as possible, and so the relentless reminders keeps showing up.
There is an "official" solution, but it involves a level of fiddling that many everyday Windows users would be disinclined to take part in. So, if you are tired of being prompted to take advantage of the (still free) upgrade to Windows 10, there is another solution.
Ultimate Outsider has a small utility you can download and install which does the fiddling for you. You can investigate and download the GWX Control Panel utility here.