If you want to remove a user from your friends list, you must first find them through Menu > Friends, by their username or Facebook name. Once you select it, next to their profile you will see the text "Following"; if you tap on it, it will give you the option to stop following them. The user will be then removed from your friends list.
In case the user continues in your friends list after removing it, we recommend that you force stop the app and then open it back again. The user should not appear on your list anymore.