The title might sound stupid but that is exactly what I am looking for. I hate to admit it but I messed up when I wanted to install Windows on my iMac (bad decision) and ended up completely deleting my whole OS X partition. How do I get it back ? I don't have any discs and can only use the Windows 10 I have on my hands. Will I have to somehow download the new El Capitan OS and put it in an USB or what exactly. Please help me.