Starting from today morning (at least in Poland) all my computers with Windws 7 started to showing a reminder, that I can reserver free future upgrade to Windows 10. Here is a Polish example:

On my home computer I registered, but on my office computer I was instructed to not reserve slot for future upgrade. However, no matter, what I do, reminder's icon in tray area (next to system clock) is always there. Closing or selecting anything brings no effect.
How to get rid of this reminder, so it would be closed permanently and never show up again?