I am running a Windows 8 32 bit guest on a fast iMac using Parallels. It turns out now that one of the programs I want to install needs 64 bits in Windows 8. My question is how can I upgrade to 64 bits without going back to scratch. My windows 8 guest was created from a Windows 7 guest using a Microsoft upgrade DVD. I do also have an upgrade DVD Windows 7 to 8 for 64 bits.