Understand whether to upgrade or clean install
Become familiar with the utilities available from the installation media
Use Migration Assistant to move user accounts and files to a new Mac
Other ways to transfer files from Mac to Mac
You may have just gotten a brand-new Mac with Mountain Lion already installed, in which case you can skip this lesson altogether (unless you want more information about transferring your files from an old machine to your new one).
If you upgrade using a Mountain Lion installation DVD or USB Flash drive, the installer presents you with a few options from which to choose before you upgrade. This lesson explains the choices you will need to make ...