I have OS X version 10.5.8 and since it isn't being supported by most companies anymore (ex. Blizzard) I wanted to upgrade to Lion. I then got a Lion USB because I read that I could download from 10.5.8 directly to Lion. However when I inserted the USB, my computer told me I couldn't download it on this version of OS X. I meet all of Lion's system requirements (excepting having snow leopard installed). So why can't I install it? Can someone give me step by step help?