The "best friend" you want to add must already be in your standard friend list.
1 - Log in & click on the "Friends"
2 - Check off the box next to the friends you want to add & click on the "Add to best friends" button appearing on the bottom of the page
To change your "Best friends", go into the "My Bests" tab and remove contacts with by clicking on the "Remove from my best friends" button on the bottom right of the page
