You can exchange foreign currency for Australian currency at banks and Foreign Exchange branches scattered throughout the Central Business District of Melbourne. Note that Foreign Exchange outlets' exchange rates are worse than banks.
You can also exchange money at most travel agents and post offices, and can find various ATM's around the city and areas. Most places are only open during weekdays, so if you need to exchnage money please do it in advance.
Melbourne Airport has a number of foreign currency exchange outlets and also many ATM cashpoints.
Destinations within Melbourne