Move or Copy items from collection to collection

In the Library

You can choose media items from any of your collections or from your independent media Items.
Choose the collection in the upper left corner (little triangle after LUNA Library)

Now you can select the media item(s) you want to copy to another collection.
Highlight all the items you want to copy together. 
In the More menu select "Copy to collection".
From the drop-down select the collection you would like to copy the media item(s) to.

Now you can select the media item(s) you want to move.
Highlight all the items you want to move together. 
In the More menu select "Move to collection".
From the drop-down select the collection you would like to move the media item(s) to.

See Also: How to delete a record or item