Deregistering a Windows 7 Home Premium Product Key

I purchased a Win 7 Home Premium Upgrade and upgraded my computer from XP to Home Premium, but then I further upgraded my pc's to Window's Ultimate and have different product keys being used for these. I am wondering if I might be able to unregister/deregister my product key so I can sell this upgrade since I now have Windows Ultimate on my pc.

I'd say it is not possible, at least not that I've heard of. You have bought the two upgrades to move from XP -> 7 HP -> 7 Ultimate, instead of paying the full price for the 7 Ultimate.

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