Hopefully this is the right place. I recently bought an older laptop with Windows 10 but is really really slow. It freezes every couple minutes and takes up to 10 minutes to boot up. I want to downgrade to Windows 8.1 (it was originally released with 7). My question is can I use the ISO creator from Microsoft and product key or do I need to buy a full retail version? I checked the driver site for the pc and it only provides drivers for 7 and 8.