Can I upgrade from Lion to Mavericks? Or must I upgrade to Mountain Lion, first?
According to the Mavericks How To Upgrade page you can update from Snow Leopard (10.6.8) Lion (10.7), or Mountain Lion(10.8) later to Mavericks (10.9) if your hardware meets the requirements, which yours does. I upgraded my 2012 MacBook Air to Mavericks about two weeks ago and the battery life is noticeably better.