This question already has an answer here:
My friend installed Windows 7 on his computer (upgrading from XP).
He wasn't sure if his processor supported x64 or not, so he installed the x86 version, just to be on the safe side.
After I looked it up, it turns out his processor does support x64, and now we want to upgrade.
The question is: is it possible to upgrade without completely re-installing the OS?
Can I? Or do I have to format the C: partition again?