Copyright generally lasts 70 years after the death of the creator or after the first year of publication depending on the type of material and/or when it was first published.
Where there are multiple authors or creators, copyright lasts for 70 years after the death of the last remaining author or creator.
Copyright cannot be renewed. Once copyright has expired the work is considered to be in the public domain and can be used without the copyright owner's permission.
More information from the Australian Copyright Council website:
The public domain consists of works that are either ineligible for copyright protection or have expired copyrights. Materials in the Public Domain are "public property" and available for anyone to use for any purpose, without requiring permission.
Works in the public domain are considered to be a part of the public's cultural heritage, anybody is entitled to make use of them for any purpose, including copying, modifying and even selling. It is even permissible to remove the original author's name if an item is in the public domain.