Replace Pro with Ultimate and move Pro to different box

[pdxireland]

Getting a free OEM W7 Ultimate x64 from work.
I installed OEM Pro on my primary machine about a month ago.
How can I replace/upgrade from Pro to Ultimate on the primary machine & use the Pro OEM key on a secondary machine now or down the road?
fmg

 

[KazeNoKoe23]

Legally speaking, you can't. If the copy of Pro you installed was an OEM copy, it's tied to the machine you activated it on.