1. Right click the toolbar and select customize
2. drag the view item from the pane of available toolbar items to your toolbar and click ok.
3. Change the view from all to unread.
4. click on your first email
5. press ctrl+A
6. press the delete key
7. change view back to all.

Made extra long because you wanted to delete only the unread.

Thanks Matt, very helpful, worked like a charm. Of course I've now realised that I meant to go back to some of unread which I hadn't had time to read when they came.... Where did they go please and is it possible to retrieve some? Sorry that I didn't think it through. Regards, Brian

usual destination is you deleted or trash folder