Changing circle shapes in Spun theme

did you make any changes?

Apparently I did, but I don’t know how/where.

Download and unpack a fresh copy of the Spun theme. FTP into your site (or whatever file management application your host provides) & upload the theme’s folder to wp-content/themes.

The circles are using this class .attachment-post-thumbnail

So you could change the radius in style.css by locating this line
.blog .hentry a .attachment-post-thumbnail

And than change the value of the radius from this:

border-radius: 180px;

To this:

border-radius: 100%;

@esmi: Thank you for your response. It seems like there should be a simpler solution, but I will keep that in mind.

@ayman: Thank you too. I changed the radius values as you suggested, and the shapes have changed, but they are still not circles. Any ideas…?

Ok, One Question so I can try to give you the best suggestion:
Did you make any changes to your style.css file apart from the one I suggested?

you seem to have changed the width here (below is te unedited original):

.hentry {
	background: #fff;
	float: left;
	margin: 10px;
	padding: 0;
	position: relative;
	table-layout:fixed;
	width: 180px;
	height: 180px;
}

use the same value for width and height

Follow the suggestion @alchymyth gave you and use the same width and height.

That solved it! Thanks so much for the help @alchymyth and @ayman.