I had Windows 8.1 (non-OEM version) installed. Yesterday I created Windows ISO from that link. When booting from this ISO (on USB stick) it allowed me to upgrad

I had Windows 8.1 (non-OEM version) installed. Yesterday I created Windows ISO from that link. When booting from this ISO (on USB stick) it allowed me to upgrade existing Win8.1 installation. After upgrade I did clean install using same ISO. During installation I skipped entering windows key. Then at first boot it activated Windows automatically.