The leadership of the party is open to feedback. Most concerns raised through this channel can be resolved simply.
You have a formal right to appeal any decision made within the party, on any matter, directly to the Executive. The Executive may elect whether or not to hear your appeal and, if they do, whether or not to uphold it. There is no higher authority within the party.
You might be able to seek recourse through the legal system over any particularly serious matter, especially if you believe party officials have committed a major violation of the party's constitution or the laws that govern it (such as the NSW Associations Incorporation Act 2009 and the Commonwealth Electoral Act 1918). In this case, you should seek independent legal advice.
Alternately, if you are fundamentally unhappy with the way the party is being run, you can attempt to force a vote for new leadership, or an amendment to the party constitution. Please read the constitution for the details of what this involves.