Basically it is just like any vBulletin site. when you click on the control panel tab, scroll down to the subscribed threads section and click on the unsubscribe tab of the thread/threads that you want to unsubscribe yourself from and you're done.
If you look to the left of the quick reply box below, you'll see options for your reply. Uncheck the 'Subscribe' box and check the last one. "Make these options default"