I have exactly the same question.
I'm looking to buy a Dell Inspiron 660 which includes a 64 bit version of Win 7 Home.
I need to have Win 7 Professional 64 bit for a program I use for work. I have the box version of Windows 7 Professional, and want to know what my next step is to upgrade to Win 7 Pro.
From what I've read, these seem to be the options for me:
1 - If I want to keep any programs that are pre-loaded, it appears as if I must buy an upgrade license. This doesn't make sense since I have a full copy purchased at retail. Then again, making sense doesn't matter when MS is involved.
2 - I can do a full install of Win 7 Pro 64 bit using the disc I have, in which case any pre-loaded programs and drivers will be erased.
If somebody can clarify what I need to do, would be most appreciated.