Are you referring to the section titled – “Calix Imperium”? The width is set to 300px. You can adjust this code to change it –
#home-feature-bg-alt .featuredpage .page,
#home-feature-bg-alt .featuredpost .post {
float: left;
margin: 0;
overflow: hidden;
padding: 0 0 5px;
width: 300px;
}
Should be line 1374 in your style.css file if you’re using an editor, if not, just search for that code and you’ll find it.