Whether you have applied for a Tourist visa or a Student visa, your stay in Australia is restricted by the regulations of the visa that you have been granted. It is important to know the expiry date of the visa, and you need to leave the country before the expiry or you need to apply for a new one. For Tourist visa, you can extend your visit to a total of twelve months or less than that.
If you have a student visa, you can opt for extending it, if there is no provision of Further Stay Restricted provision levied on the visa. You can go through the grant information to have a glimpse of this. While extending your duration of stay there are few options that you can consider. You can apply for a new Student Visa or a Visitor Visa, Work Visa or a Visa for General Skilled Migration.