I've tried changing language to Australian English but it keeps reverting to US English, is there anything I can do to change it permanently?

I am using version on OSX 10.6.8
I’m having trouble in the writer component

Please check the settings in LibreOffice > Preferences > Languages Settings and see if there is Australian English set as your default language.

If this is not the solution, please explain (step by step) how you changed from US English to Australian English.

Thank-you. I have followed these steps and it has changed the spellcheck to Australian for new documents. When I open previous created documents they have USA spelling so I have to change it in preferences again.

How do you change preferences for pre-existing documents?