Go to your profile settings and then click on the tab on the right that says "watched threads". It will show you all the threads that you are currently watching (duh lel) at the bottom of the page it says "Show all Threads" (it is somewhat small so you might have to look for it.) Click that and once you do little boxes will appear next to all the threads on the list. If you click on the boxes a check will come up. After you check all the threads you want to stop getting alerts for you once again go to the bottom of the page where it will ask "what do you wish to do with the marked threads" or something like that. If you click on that a little menu will pop up with a couple options, one of them being to "unwatch" the thread. Then Tada