If you mean Sydney, Australia :) I think this page may help you:
It has contact details of the Sydney office of the US Embassy, and should be able to tell you if you need to deal with the central Canberra-based office or whether you can renew it locally.
Here's the info you'll need to fill out the paperwork in any case:
Good luck! over 6 years agoAnswered by Lou Hutton via WorldNomads.com