Upgrades can often cause more problems than they're worth. Programs won't work, the system can be slow. I find the best way to install is to do a clean install, without formatting. Your old installation will be moved to a folder called windows.old on your hard drive, which you can access to move your personal files over to your new installation, and then you can go into the Program Files folder and be presented with a list of applications to reinstall. Once you're done that, run disk cleanup as an admin and use it to cleanup "Previous Windows Installations" which will delete the several GB large folder.