Since some new versions of Windows install new file systems, in addition to replacing most, if not all the program and support files, it is recommended that you simply reformat your hard disk in order to completely remove whatever version of Windows you've just installed.
if you're about to install a new version of Windows, it's a great idea to do a full backup of every file on your hard disk before you actually perform the upgrade.
Like i always say though.You are doing what you do at YOUR OWN risk