Hi,
Upgrading from Windows 7 Ultimate 32 bit to 64 bit will require a custom install. The process will not require much effort since it's the same as doing a clean install and reinstalling drivers and applications.
You may refer to Andre Da Costa's article on ***How to: Perform a custom installation of Windows***.
See section for Windows 7.
To read it's thread for other additional tips on Windows 7 64 bit clean install, click the link below.
Feel free to post back should you need further assistance.