Yes, you can. It will be almost like doing a fresh install - Windows will install in a new folder & your previous 32-bit Windows folder will get renamed to Windows.old in the process (the latter can be deleted in most cases to recover the space).
Going from another user's related experience click here, you should have everything else pretty much untouched, although do a thorough prior backup of your emails, data, music, etc just to be on the safe side. You may also need to reinstall some/all your programs & afresh.
Please note that some of your older hardware (especially peripherals like printers, scanners & similar) may not work, & you'll need to download 64-bit drivers (if available) to get them to run as normal. Any particular reason for wanting to move to 64-bit? G