Sorry I misunderstood your problem. I thought LC is the model element child of Appliance, but in fact LC is only contained by Appliance in view and they have no real parent-child relationship, and thus you won’t see the Delete (Not Delete Child) menu item.
And unfortunately no matter you choose delete or delete view only, the contained diagram elements must also get deleted altogether even they are not parent and children.
So, what you need to do is to break the view containment relationship of LC from Appliance. But in VP’s sequence diagram, a lifeline cannot leave its frame if it has any messages connecting to other lifelines that are not in the same frame. That means you must first make LC free of those messages before you can move it out. You can either:
- Delete all LC’s messages, move LC out of Appliance, and then recreate them afterwards.
- Temporarily move the messages to another lifeline, and move them back after you moved LC out of Appliance. You can drag the end point of a message to attach it to another lifeline.
Hope this could help to solve your problem.