So I asked a few questions about the Windows 10 upgrade using Microsoft's Answer Desk and this is what I found out...
- you need an existing install of windows 7 or 8.1 excluding enterprise editions
- the existing install must be genuine
- must be an upgrade install, not clean.
- your windows product key will work for windows 10 after windows 10 has synced the key (activated)
- after the key has been synced (activated) clean Install will be possible.
Well that's my understanding of the whole thing anyway, hope this helps clear up some of the confusion.