As far as i read it you get the upgrade free the first year iof you own win7 or windows8
You do not get it if either Win7 or Win8 are enterprise or RT-Starter editions.
The way i see it once hardware is changed the SSID needs to be changed or you return back to your previous OS.
However i think once you upgraded you will keep your license for a lifetime meaning that if you change hardware you will still be able to use windows10
If not it would be ironic to try to get most of the users off OS like Win7 and below to use windows10.
