In sprint planning we create sub-items. 

1) I have created a few sub-items under a story I later decided should be split.
2) I also accidently created a sub-item of a sub-item and wanted to move it up a level (but not to the story level).

How do I move the sub-items once we've started the sprint and are in planning?  I can't work out how to do it.

I think it may be possible on the backlog view but the current sprint isn't shown on the backlog view.  I've tried swimlanes on and off, sub-tasks shown and not shown.  I've tried to associate the 'destination' story with sub-item but it didn't appear in the list (presumably because it already has a parent).