How do I change the DVD reader back to the right region code?

I went to Australia and watched a few DVD's from over there and got the pop up saying to change the region code inorder to watch the movie. I did this a few times not knowing that it would just stick to the last region code after changing it 5 times. I am now back in Canada and can't watch any DVD's because my laptop is stuck on the Australian region code. Is there any why I can get it back to the right region code?

Thanks!!!