If you go to the person you want to edit, then go to "Change or Delete", you should have the ability to make a partner an "extra" or "ex". If you go to the "Partner" tab, you'll also have the ability to change the relationship to your existing partners.
If you just want to delete the person all together, then it's just the same as anyone else. Go to "Change or Delete" then click "Delete 'whatever the person's name is'". Unless they're existence is crucial to keeping the tree together, then you should be able to do so.
