It seems that the sizes of these images are hard-coded but I might be wrong. You could use CSS to scale them larger but it would change the image quality for the worse. Here's some sample code so you can see exactly how it looks:
img.attachment-it-thumbnail {width:150px; height:125px;}
I would recommend leaving them as they are but if you do want to make them stand out a bit more try something like the code below. You'll need to try to open the page in a newish version of firefox or safari otherwise you won't be able to see the difference.
img.attachment-it-thumbnail {-webkit-transform: rotate(5deg); -moz-transform: rotate(5deg); transform: rotate(5deg); margin-right:10px;}
lh