Ingoing or Outgoing relatshps in the screen Change Entity Type: Definition.
If you are in the screen Display Entity Type: Definition, click on Display<->Change to switch to maintain mode.
The screen Maintain Ingoing (or Outgoing) Relationship appears. A list of existing ingoing (outgoing) relationships is displayed.
Position the cursor on the relationship you wish to delete. If you double-click with the mouse, the screen Maintain Relationship: Definition appears.
Choose Relationship