None. You must erase the drive, then reinstall OS X. The procedure depends partly on what model you have and if it is able to perform a Network Install.
Despite what John has stated, I think it's widely understood that a "clean install" simply means and "Erase and install." We know what it means, so don't dwell on this piece of terminology.
Here's how you do a Network Install. Your computer meets the needed requirements:
Install OS X Using Network Recovery
Be sure you have backed up your files because the following procedure will remove everything from the hard drive.
Boot to the Network Recovery Server:
Restart the computer and after the chime press and hold down the COMMAND-OPTION- R keys until a globe appears on the screen. Wait patiently - 15-20 minutes - until the Recovery main menu appears.
Partition and Format the hard drive:
- Select Disk Utility from the main menu and click on the Continue button.
- After DU loads select your newly installed hard drive (this is the out-dented entry with the mfgr.'s ID and size) from the left side list. Click on the Partition tab in the DU main window.
- Under the Volume Scheme heading set the number of partitions from the drop down menu to one. Click on the Options button, set the partition scheme to GUID then click on the OK button. Set the format type to Mac OS Extended (Journaled.) Click on the Apply button and wait until the process has completed. Quit DU and return to the main menu.
Reinstall OS X: Select Reinstall OS X and click on the Continue button. Be sure to select the correct drive to use if you have more than one.
Note: You will need an active Internet connection. I suggest using Ethernet if possible because it is three times faster than wireless.
This should restore the version of OS X originally pre-installed on the computer.
If you wish to simply wipe the disk and reinstall the version you have already installed, then do this:
Install or Reinstall OS X from Scratch
Be sure you have backed up your files 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.
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.) Optionally, 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 OS X: Select Reinstall OS X 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.
This should install the version of OS X that you had installed.
