You have installed a 32-bit version of Windows 7. A 64-bit Windows 7 can legally be found here
. As the image taken from that site here shows, you have to choose if you want to download a 32-bit or 64-bit Windows 7.
You have to do a clean install, a 32-bit system can not be upgraded to a 64-bit system.
Kari EDIT: Please remember that free downloads will only be available until August 20, 2009.