To unfriend someone:
- Go to that person's profile (timeline and even old profile)
- Hover over the Friends box at the top of their profile (timeline and old profile )
- Click Unfriend
- A dialog box pops up. Click "Remove from Friends"
Viola! You're done.
Note: If you choose to unfriend someone, you will be removed from that person's friends list as well. If you want to be friends with this person again, you'll need to send a new friend request.