Expatriation is your right and if you are an Australian citizen over the age of 18 renouncing your Australian citizenship in favor of acquiring citizenship elsewhere is legal and possible. However, as Australia has participated in the United Nations Convention on the Reduction of Statelessness, it is necessary that all Australian citizens who wish to renounce citizenship have already gained citizenship elsewhere. If this is not possible until the individual has renounced their Australian passport, then evidence that citizenship of another country will be granted once the Australian passport has been surrendered will be required.
Children under the age of 18 may also be permitted to revoke their passport alongside their parent or guardian's application providing that the child does not have a further legal guardian or parent who will remain an Australian citizen and any application to give up the child's citizenship will leave them stateless.
Applications for children under 16 years of age must be made by a parent or legal guardian.