It’s free to update your passport provided you do so within 1 year of your wedding, divorce or legal name change. Your passport will be updated with your new name, however your expiry date will remain as per your existing passport.  If your passport is close to expiry you may want your new passport to be issued for another 10 years by paying the full fee.
 
Free service – keeping current expiry date
If you are updating your passport with your new name and keeping the current expiry date then you need to complete a new application form.  You can pick this up from any post office.  You are unable to complete your application online and will also need to visit a passport office to lodge your application.

Renewing your passport for another 10 years
If you are paying the passport application fee to renew your passport for another 10 years then you can complete the application online.

A standard 32 page passport valid for 10 years cost $208 as at 1 July 2008.  If you prefer you can also pick up a passport application form at a post office.  You will also need to have a brief passport interview regardless if you chose to enter your details online or on a paper copy.

Visit the Australian Passport website