Before going further, here are some key points to be aware of:
If you are currently running a32-bit version of Windows (regardless of whether it's XP, Vista, Windows 7, or Windows 8), then you cannot upgrade directly to 64-bit Windows-- instead you will need to do a clean install of 64-bit Windows 7 or 64-bit Windows 8.
A clean install means your files, settings, and installed programs will not be preserved automatically during the installation process.
Instead, you will need to backup your files and locate your program install materials and then restore or re-install them manually after installing the 64-bit version of Windows 7 or the 64-bit version of Windows 8.
If you purchased a retail version of Windows 7 or Windows 8, then a 64-bit version will be included; your key will unlock both. If your computer came with Windows 7 or Windows 8, on the other hand, then you may or may not have a 64-bit version as part of the restore and install discs that are typically included with your computer; check the discs that came with your computer or contact your computer's manufacturer to be sure. If you don't have this option, visit the Microsoft Store.