Windows 7 to 8.1 preview to ??? UPDATED

I just downloaded the ISO to my 7 computer and have it ready to install and everything. If I go from Windows 7 to Windows 8.1 preview (I don't care if I have to reinstall crap (I've got it figured out) will 8.1 preview go to 8.1 final for free?

UPDATE But what if I have a Windows 8 key? If I upgrade from 7 to 8.1 preview then want to go to final can I use a Windows 8 key to get it free?