What's the simplest way to move a Windows 8 Pro license form one machine to another one?

I have one laptop with a Win 8 Pro license, and another one with Windows 8 OEM. How can I exchange the licenses? I've seen another answers pointing to MS Phone Support, but those don't mention the downgrade path (the first laptop will downgrade from 8 Pro to 8, and the second would be upgraded to Pro)

Is this possible? Are there any alteatives, besides MS Phone support?

Thanks,