Du kan hente win 8 og så installere den med din nøgle, derefter opdateres til 8.1 eller hvis du har en nøgle til win 8.1 så kan den hentes.
fra link
Here’s the most important thing you need to know:
Windows 8 and Windows 8.1 have different product keys.
That is, if you have a Windows 8 license and attempt to install Windows 8.1 with your Windows 8 product key, you’ll receive an “invalid product key” message.
You must instead install Windows 8, provide your Windows 8 product key, and then update to Windows 8.1 from within Windows 8. Yes, the Windows 8.1 upgrade is free if you’re using Windows 8, so this is just unnecessary pain.
Likewise, if you have a Windows 8.1 license, your Windows 8.1 key won’t work with a Windows 8 disc. You’ll need Windows 8.1 installation media to use a Windows 8.1 product key.
First, visit the Upgrade Windows with only a product key page on Microsoft’s website. Click the Install Windows 8.1 button if you have a Windows 8.1 product key or click Install Windows 8 if you have a Windows 8 product key.