How do I set Featured Image size on Classifieds?

I really like your Classifieds plugin, but I have a problem with Featured Image size... On Index page my featured images are showing in full size instead of resized... I had a look and I think that set size for featured images is width: 298px and height: 248px but all my featured images are showing in full size as uploaded... How can I force the images to crop to set 298x248?

Look forward to your reply.

Jass