Want to use DO external image viewer

During my initial setup I've specified that I didn't want to view my images in DO..

But now I do want that (I prefer that viewer to that of Windows 7).
How can I view my images in the external viewer of DO?

(I've searched the forums, but have not found what I needed)..

See the FAQs:

Viewer and Viewer Plugins[ul][li] Stop the Opus image viewer from being used by default[/li]
[li] Use the Opus image viewer inside or outside of Opus[/li][/ul]