I have an old I-Mac7.1 that still has version 10.4.11 operating system on it. It has served me well, but I can't add new software or hardware without having a newer OS. What would I have to do to upgrade to one of the big cats, preferalby Lion? I have 2 GHz processor speed, 1 processor, 2 cores, 4MB of L2 Cache, 2 GB of memory, and an external 1 TB of storage. Any suggestions? Be gentle; I'm new at this stuff. Thanks.