How do I, on OSX, completely wipe out my computer (as if it was fresh from the store) so I can download Lion from the Mac App Store. I don't think I have any OS disc. If I download Lion from the Mac App store will it give me the option to wipe my disk on install? My iMac is just running worse and worse each day. I use it for development and it is getting to the point where XCode takes forever to load and then the mouse can barely move, etc.