Change featured image size in code

I know this should be simple but I can’t seem to figure it out. I’m just trying to change the featured image size on the “People” pages from 400×225 to 400×400 (it auto resizes). I’ve used Firebug and searched my code but I’m stumped. My site has a coming soon page up so here’s a link to the theme’s demo site. And for some reason its already set at 400×400 but I’m assuming the code for it should be in the same place. Where’s the code determining this?

http://demos.churchthemes.com/resurrect/people-profiles/

Thanks!