image size issue

the images (jpg) that i upload/insert to a page, all show up in thumbnail size. the image is much larger and i make it to use the full size, but they still show up as thumbnail. if i select “attachment page” in the media option, then i can get the bigger image by clicking the image. but i want to show up larger in the first place. i believe this is an issue with the theme. see: http://parsology.net/special-events/. any ideas how to fix this? thanks.