It can't. But the people get to vote in politicians who will put the referendum questions they want put. No. The crown didn't change 36 years ago. The Queen remains Australia's Head of State. Which ones are you most concerned about? We do get to choose our head of state. The Constitution says who the head of state is, and the people get to amend the constitution, via their popularly elected representatives. Not at the moment. Why do you ask?