I'm thinking about selling my 2010 Macbook Air in the next few days before WWDC. It came with Snow Leopard but I upgraded to Lion through the App Store. I'm not entirely new to mac and know how to do most basic stuff, but I would like you guys to help me with reinstalling Lion (I don't need to install Snow Leopard again, do I?) and securely erasing my ssd before putting it up for sale. I don't need a very detailed description, just a step by step guide or something about how to do it in the right order.