How Do I Install OS X Lion?
OS X Lion can currently only be purchased from the Mac App Store. You will need a computer running Mac OS X Snow Leopard to access the App Store.
Purchase OS X Lion like any other app and it will begin downloading. It may take a while - the download is approximately 4GB. Once the download has finished, there will be an Install OS X Lion icon in your dock. Simply click the icon to launch the app and the installer will begin.