How do I restore factory settings on my MacBook Air?

Question

I have sold my MacBook Air (bought in August 2011) and I need to restore factory settings.  Can someone please help?

Answer 1

As quoted from apple member Kappy
Boot from the Recovery HD by restarting the computer and after the chime press and hold down the COMMAND and "R" keys until the computer starts from the Recovery HD. Select Disk Utility from the main menu and click on the Continue button.
2. After DU loads select your hard drive (this is the entry with the mfgr.'s ID and size) from the left side list. Click on the Partition tab in the DU main window.
3. Under the Volume Scheme heading set the number of partitions from the drop down menu to one. Set the format type to Mac OS Extended (Journaled.) Click on the Options button, set the partition scheme to GUID then click on the OK button. Click on the Partition button and wait until the process has completed.
4. Select the volume you just created (this is the sub-entry under the drive entry) from the left side list. Click on the Erase tab in the DU main window.
5. Set the format type to Mac OS Extended (Journaled.) Click on the Options button, check the button for Zero Data and click on OK to return to the Erase window.
6. Click on the Erase button. The format process can take up to several hours depending upon the drive size.
At this point all your data are securely removed. You can shut down the computer or reinstall Lion from the main menu.
https://discussions.apple.com/thread/3269952?start=0&tstart=0