UPDATED VERSION:

1. Go to your family tree
2. Click the person you want to add to
3. Click "Profile"
4. At the top right of the profile it should have a "tools" button and an "Edit" button
5. Click "Edit" and three different buttons should come down from there. One is an "edit relationship" or "add relationship" button.
6. Click the relationship button and it should pull up a screen with the current parents and that is where you can change them to adoptive or step parents or biological parents. 
7. To add a new parent click "add alternative father" or "add alternative mother" 

Hopefully this helps! We were looking for the new way to do it and nobody had the updated version yet.