You can delete subitems from the subitem overview.
To goto the subitem overview click Subitem.
How to delete a sub-item:
You see a dialog box with a security query. Confirm this query.
How to delete all sub-items for an item:
Confirm the query.
The item quantity is now
When you delete all sub-items for an item, the item is not deleted. You can only delete items on the item overview.