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I've done an install of Windows 7 Ultimate on my laptop when I meant to install Pro - i.e. I've already used the Ultimate license on another box and want the laptop to run Pro for which I've got keys spare.

Is there a way to change the SKU of the installed version to downgrade it so that I can use my Pro key. I've got a fair bit of stuff on it and would like to avoid re-installing the OS if I can.

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up vote 2 down vote accepted

See this article : Downgrade: Change Windows 7 Ultimate to Premium or Professional.

It explains in detail how, with changing a simple registry setting, you can fool Win7 Ultimate into agreeing to install Professional as an "upgrade".

In-place upgrading keeps all installed applications and settings.
But as always: Before doing such an operation, ensure you have backups.

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Fantastic - worked perfectly. – Chris W Jun 3 '10 at 11:30

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