Windows 10 won't take no for an answer

Once again Microsoft has not failed to depress.  I have noted the "get windows 10" nags over the recent days, dismissing them without a thought, but today they drop this on my desktop with no way to cancel it.  I have 2 choices, install windows 10 now, or later.  Not a cancel button, or a close button anywhere to be seen.  This is like some a-hole telemarketer who keeps calling back every 5 minutes because you at one point, when you may have been drunk, expressed the smallest amount of interest in the magazine subscription he was pedaling.  I have work to do, and backups running, but when I get done, and can reboot, I will give this a try...