The latest versions of the Mac OS X operating system are not available as DVDs, but you can still boot your computer to an installation volume and run different Disk Utility operations. For example, if you need to reinstall Mac OS X on a MacBook in your office and want to clear all the data off of the computer, you can use Disk Utility to reformat the laptop’s internal hard drive. Before reformatting the MacBook, make sure to back up all data that you want to retain.
Backup all your data to an external HD
Restart your MacBook and hold down the Command and R keys when the gray startup screen appears.
Click on the “Disk Utility” option and then click “Continue.”
Highlight your MacBook’s internal hard drive from the list on the left side of the window.
Go to the Erase tab at the top of the window.
Set the format type to “Mac OS Extended (Journaled),” and then enter a name for the hard drive that will be reformatted.
Click the “Erase” button.
Open the Disk Utility menu when the reformatting process is finished, and click “Quit Disk Utility.”
Click on “Reinstall Mac OS X” to begin the process of installing a fresh copy of the operating system.