I'm assuming you are referring to a thread in which you have posted a response to? And now do not want to continue to receive notifications of updates to that thread?
If so, go into your profile from the tab above. On the left side menu select Notifications.
There you will see a list of boards and threads you are receiving notices from. Simply go down the list and check the box on the right side and select Unnotify.
If it's something else, let us know.
Hope this helps. I'm answering for Liz, she is either at work or sleeping after work.