Category thumbnail

Hi guys,
I have a problem with my site. On category pages like this:
http://www.scuderiaferrari.cz/category/novinky/
every thumbnail image has a different size, and I need all the thumbnails to have a same size.
Is there anybody who could tell me what to do? Please don´t notice Czech language, it´s my czech site, just have a look at the images.
It´s a big problem for me.
I´m using a CarMag free template if you need to know.
I would be very grateful if anybody could tell me what to do with this.
Thanks a lot