It is simply not possible to upgrade from 32-bit to 64-bit. The changes between the two are substantial enough that nearly every system file and configuration would need to be replaced in ways that no installer could calculate. In essence, there are too many variables at work. While I know what you mean by upgrading Windows XP to Windows 8, as you would retain none of your settings, but still have working files on the drive, it really is a doozy. At this point, to initiate this type of "upgrade", you will really want to do a full install and not an upgrade. While this complicates things quite a bit, because you already have a valid copy of Windows XP, and just not the 64-bit version, and do not really want to retain your system settings...