You click on the big green button on the right hand side of your profile. To remove a friend, go on their profile and on the same place as the add button was or you can go to the control button.
Based on my experience, this add friend button is a "one-way street." I just realized today that someone I am someone's friend, but they are not added as my friend. I suggest that we make this friendship a "two-way street." This way we will all know who our friends are, and it will be a mutual friendship. : )