From time to time, there may appear to be duplicates of the same person on your family tree. In most cases, this happens when hints are merged on the tree incorrectly. To remove a duplicate person, go to the profile of the person you want to delete and select the 'Relations' tab.
While hovering over someone in the relations tab you will see a 'broken link' icon which will allow you to remove them from that family or the entire tree.