IMac PPC :: Upgrade And Reformat It From Leopard To Lion?

i have an iMac on 10.5.? something.. and i want to get it back to factory setting and upgrade it to lion, as im half way to selling it to a friend. It needs reformatting asap really as he already managed to get that flash trojan on in within his first 2 days of having it, and its already had some mileage that could do with being reset anyway. i also what what i wanted to know how to upgrade to lion without having to get snow leopard as well. i know i need to install some more ram which im in the process of getting from Crucial.com. i just need to know about how to bypass snow leopard.