When a woman marries, it is a custom for her to assume the surname of her husband. There is no law that says she has to. She may keep her “maiden” (pre-marriage) name or combine her own surname with that of her husband. Her husband has the same range of choices.
If a woman who used her husband’s (or her former husband’s) name on her marriage certificate wishes to begin using her maiden name again, all she needs to do is to start using that name again. As her birth certificate (or perhaps her citizenship certificate) will still be in her maiden name, she has written proof of her maiden name. However, it is important that she let people know.
If you marry overseas, it is important to note that some organisations will not accept overseas marriage certificates as proof of your right to use your spouse’s surname. This means that you need to provide proof that you have changed your name, in the form of a new birth certificate or a change of name certificate (to obtain these certificates, you must apply to register your new name with the Registry of Births, Deaths and Marriages; see “Registering a new name”).
In proceedings under the Family Law Act 1975 (Cth) (“FLA”), if any party changes their name after the start of a case, the court and the other parties must be provided with written notice of the change of name (see reg 24.03 Family Law Rules 2004 (Cth)).