There is no definitive way to deal with vandalism, however here's a list of suggested steps to take to deal with any vandalism.
It's important to establish if mistakes were made or it was intentional vandalism, often it is better to err on the side of caution and assume it was a beginner mistake.
What to do if it is a mistake?
Contact the person that made the edits and ask them if they need help.
If they don't respond you can email the talk-au mailing list to ask for help in this matter.
Suggest something along the lines of:
Your changes to the OpenStreetMap have been noticed. OpenStreetmap is a serious project, not a place to immortalise your friends. Please join us to add real data to the map - put your favourite fast food joints on, improve the map and not deface it. OpenStreetMap has tools to remove all your work in one move, and this weekend we intend to remove all of your changes."
When you contact the user, be polite it may just be a simple error on their part.
What to do if it is vandalism?
Contact Revert Au with the user name and list of changesets that are possible vandalism. If you do not provide the changesets then all will be taken to need reverting.
Email (email@example.com) asking for a block on the user account to try and prevent further vandalism.
If there is only a small number of malicious edits you could try to revert them yourself, by editing or deleting as needed.
If the vandalism is more extensive DO NOT make any changes in the affected area, this makes reverting the changes more difficult, you will need to contact the talk, dev, or data lists to ask someone that performs bulk reverts a list of changesets that need to be reverted.