Install or Reinstall Lion/Mountain Lion from Scratch
Be sure you backup your files to an external drive or second internal drive because the following procedure will remove everything from the hard drive.
Boot to the Recovery HD:
Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.
Erase the hard drive:
1. Select Disk Utility from the main menu and click on the Continue button.
2. After DU loads select your startup volume (usually Macintosh HD) from the
left side list. Click on the Erase tab in the DU main window.
3. Set the format type to Mac OS Extended (Journaled.) Click on
the Security button and set the Zero Data option to one-pass. Click on
the Erase button and wait until the process has completed.
4. Quit DU and return to the main menu.
Reinstall Lion/Mountain Lion: Select Reinstall Lion/Mountain Lion and click on the Install button.
Note: You will need an active Internet connection. I suggest using Ethernet if possible
because it is three times faster than wireless.
Once the OS is installed the computer will normally restart. Before it does shut down the computer.
Many thanks. I have no files on the computer that I want to keep; indeed I want to get it back as near as possible to its original unused state and so that it will come on with the original set up screen. Am i right that i do not therefore need to make a back up? I
I have OS X 10.8.4. Presumably the recovery downloads this from Apple. Will it automatically download the same. I don't want to risk getting 10.8.5.
Of course all that I would really like to do is remove the user data (name& password) but it seems that there is no simpler way.
My macbook air has no ethernet connection, so i can only do this with wi-fi. Any idea roughly how long it will take?