Hi
you can use the upgrade but not all cds have the upgrade option
but you may still have to change some settings and reinstall some programs
or you can do a anytime windows upgrade

read more hear
http://windowsteamblog.com/windows/b/windows7/archive/2009/07/31/the-windows-anytime-upgrade-experience-for-windows-7.aspxClick on Start, then type in anytime upgrade into the search box
and click on Windows Anytime Upgrade