SR-71 Blackbird said:
If it is a sticker from the computer that has the key that is oem and not transferable.
He's not transferring though just changing from 32 bit to 64 bit and the product keys are interchangeable between them.
You'll be fine just downloading the 64 bit version and activating with your current key ( Just make sure you get the same VERSION (ie. Home Premium, PRofessional, Ultimate as Keys for these are not interchangeable !)