Home Sharing - how to get music files to transfer from one computer to another...

I have two computers in my home authorised for Home Sharing - I have no problems locating the other library on either of my computers. However, when I am on iTunes in Computer A and I click onto Computer B's music library (so that I can transfer music file to Computer A) I am unable to move Computer B's music into Computer A. I have both iTunes open on each computer and ther are both using the same Wifi connection.

In iTunes Help, it says:

- select the music files that I want to share into Computer A. (this bit I can do).

- in the 'show' menu at the bottom of the iTunes window, select 'items not in my library'. This is where I run into trouble - there does not appear to be any such menu!

- select items I wish to import, then click on 'import'. - again, no such button appears to exist!

I have updated my iTunes software to the latest version available on both computers. This is very frustrating for something that should be quite simple - I would very much appreciate any suggestions or solutions...