Categories thumbs

Hi,

I would like to show thumbnails of my categories instead of a list of articles. Unfortunately the people behind the theme doesn’t have a support or a forum section, so I can’t ask them.

This is their example site with a view of the categorie for Art: http://demo.graphpaperpress.com/workaholic/category/art/

And this come up when I’m trying to do the same thing:
http://bremell.com/workaholic/ (only an image, working local).
And yes, I’m linking to the categorie Webbdesign, subnav to Portfolio.

Can you please help me?

Regards,

Pir