Look for the words "thread tools" up above the thread on the right, and click on the little diamond next to it, there's the option to "unsubscribe to thread" there. If you have a lot to do, you can also do it under "settings" "my subscriptions". Open up the file where you have yours stored, and they will all be listed, and they will have a check box to the right of each one. Put a check in each of them that you want to delete, then scroll down to "selected threads", put a dot in "delete subscription(s)", then click "GO". All that you checked will be deleted.