When you are in a topic and want to be notified about future updates to the topic, you can do this by scrolling down to the bottom of the forum and clicking on the subscribe button (you need to be logged in to see this button!)

Once you clicked this button you will receive email updates. These emails will also provide you with a link to unsubscribe from the updates.

You can also unsubscribe by returning to the thread, scrolling to the bottom and then clicking the unsubscribe button.