There are several ways to unfriend a friend in Facebook.
1.Go to your own profile page. Select the "Friends" Tab, find out the one whom you want to unfriend. Beside their name, you will get a "Friends" tab with a drop down list option. There at the end of the list, there is an option for "unfriend". Select that and you are done.
2. Go to the particular Friend's profile. There in the Cover Photo area, there will be a tab named "Friends", where you would get a drop down list icon, click on it, select "unfriend".