How can I erase the data from my Macbook without losing my recent OS? I'm going to sell my Macbook Pro and want to remove all of the data before doing so. I have the OS Lion installed but my machine came with Snow Leopard. How can I remove everything and restore it to basically just the OS without losing Lion? I want to sell the machine with Lion. Thanks.
Apple provides instructions on erasing and reinstalling OS X, so the system will be as it was when it came from the factory: http://support.apple.com/kb/PH4439

These instructions guide you through reformatting the drive and reinstalling OS X via Recovery.