You can only sever a joint tenancy if you own a property with co-owners and the title deed to the property shows that the owners are joint tenants.
Documents must be prepared and lodged at the Department of Lands directing the Registrar General to change the co-owners from being joint tenants to tenants-in-common.
There is no stamp duty payable as long as the portion of the property you hold isn’t changed.
It is possible to sever a joint tenancy without the consent of the other co-owners.
If you own a property with one or more co-owners and you hold the property as joint tenants, then on your death it will pass to the surviving joint tenants regardless of what you state in your will. You may not want the other co-owners to receive your share on your death.
By severing the joint tenancy, you are making the co-owners tenants-in-common instead of joint tenants, and therefore you’re able to leave your share of the property to anyone you like.
You may have inherited a property with your siblings as joint tenants but would prefer your share of the property to go to your spouse or children. That will only happen if you sever the joint tenancy with your brothers and sisters.
You may have purchased your principal place of residence or on it an investment property with your current spouse or partner as joint tenants. However, if you have children from a previous relationship and you wish to provide them with an inheritance from the property then you will need to sever the joint tenancy with your current spouse or partner. Otherwise, it will go to them regardless of what you say in your will.
You may have separated from your spouse or partner and no longer want them to receive a property that you own with them as joint tenants. By severing the joint tenancy, you can specify in your will who gets your interest in the property.
http://www.austlii.edu.au/au/legis/nsw/consol_act/rpa1900178/s97.html