Cropping Thumbnails

Hello, thank you for this great theme. I am trying to display a product line. I select the featured image, include the page in a category, make a page displaying that category, but when I go to the category page, the thumbnail is not cropped, but rather all crammed into the 180×180 space. How can I have the image cropped?

I’ve read all over the web on this and haven’t found a conclusion. I tried cropping with the built-in editor (which writes to 150×150) and I have tried two other plug-ins as well (“Crop Thumbnails” and “Post Thumbnail Editor”). You can see an example here:

http://cambodia.rajanacrafts.org/?cat=2