Simple Wp Theme Thumbnail Fix

I just want my aspect ratio of the thumbnails in this WP theme to be fixed.

As you can see in the main page of http://wwnn.co.uk/, the images were stretched and scaled to 402×210px.

I just want the images to be like this: http://www.dailyworldbuzz.com/

The images their were cropped and were not scaled nor stretched. I just want the thumbnails to be cropped and fit the thumbnail size in the main page.

I hope you get what I mean.