Windows 10 will be free for all Windows 7/8/8.1 owners during it's first year

Microsoft is telling in their event on Jan 21st 2015 Windows 10 will be free (no cost!) for all of you with Windows 7/8/8.1. However when Windows 10 RTM (release To Manufacturing) -version is out there later this year you have 12 months period to make up your mind. After that free upgrade will not be possible (I guess?). So you'd better be quick! (That's what Microsoft wants!)

I guess a fresh install will be available since Microsoft wants everybody to upgrade - no matter if the hard disk is empty or not. So that takes me to another thought. Where can I download Windows 10 RTM -version and which key do I need to make this free version to work? Microsoft doesn't want to see people using illegal versions of Windows 10, does it? So do I simply look under my laptop and type in my Windows 8 key number when Windows 10 is asking it? I don't want to visit Microsoft Store app in Windows 8.1 and start upgrade from there! By the way Apple doesn't want any keys or numbers. My Mac has free OS X 10.10 with fresh install.

No Consumer Preview? I only have the old Technical Preview to show you :( .