Once you’ve decided that you want to “unfriend” someone on Facebook, here’s a step by step process to remove them from your online life forever.
To unfriend someone:
- Go to that person’s profile (timeline)
- Hover over the Friends box at the top of their profile (timeline)
- Click Unfriend
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.
Source: https://www.facebook.com/help/?faq=172936839431357