Hi Arindam
Not sure if your referring to pages that you have marked as favourites or liked here in SCN, if you are you will need to go to the original post that you marked as a favourite or liked and simply unlike the post by pressing the like button that you must have originally pressed when you first read the posting.
This can be found at the top of the page just to the right of the posting.
To stop email notification, simply press the "stop email notifications" link in the "Actions" pane on the top right of the page.
Hope this helps.
Majid