Featured image resizing

Hi there Just installed your theme on my site and have been trying to get it customised to how i want it and am struggling a little bit here.. The site is www.gingermilk.co.uk As you can see from the main page, the featured images are all large.. How do i go about setting them at a smaller size? I see there is already a post about wrapping the text so will apply that once i get the image size sorted out..