Type Anytime Upgrade in the Search programs and files box in the Start menu and click on the Windows Anytime Upgrade icon. From there, you can buy an Anytime Upgrade to Windows 7 Ultimate. Then you can enter your Anytime Upgrade product key and perform a simple
upgrade to Windows 7 Ultimate.
If you are in Australia, Belgium, Canada, France, Germany, Italy, Japan, the Netherlands, Spain, Sweden, Switzerland, the UK, and the US you can use Anytime Upgrade. If not you will need to buy the version of Windows 7 you want.