Change square thumbnail to thumbnail in featured item "theme rhytmn fall"

Good afternoon,
I'm trying to change the display of the images in "featured-item" probe and changing parts of the code in the files show.php, browse.php, but this does not work.
I think that is a function which controls this aspect but I failed to identify where it is set to the square appearance. What I want is to display all images as thumbnails.

The theme used is rhythm ... falls
I add some pictures to illustrate my problem.

pictures of the problem

You'll find the function that's creating that output in the theme's custom.php file; it's called rhythm_display_random_featured_item_squarethumb.

You should see that it's using the function item_square_thumbnail, and simply changing that call to item_thumbnail should do what you're asking for.