Can i update my iMac?

I just got my hands on an iMac and I am not sure what exactly to do with it. It is not new, i know that for a fact. So can someone assist me and let me know if I can update it anymore or what can I exactly to do it to bring it as close as possible to being "up-to-date"

System Version:Mac OS X 10.4.11 (8S165)

Kernel Version:Darwin 8.11.0

Machine Name:iMac G5

Machine Model:PowerMac8,1

CPU Type:PowerPC G5 (3.0)

Number Of CPUs:1

CPU Speed:1.8 GHz

L2 Cache (per CPU):512 KB

Memory:1 GB

Bus Speed:600 MHz

Boot ROM Version:5.2.2f4