[Theme: Beardsley] removing the thumbnail images

Whenever I post images using this theme the images are all thumbnails. I tried editing the css and the images become the size i want but they are blurry like its stretching the thumbnails out to the size i want. I cant find anything regarding thumbnails in the php code. Can anyone give me a hand? You can see my issue at https://www.lacyrosexo.com

https://www.ads-software.com/extend/themes/beardsley/