Hello,

I saw the screenshot you attached. The thumbnails of the blog images are controlled by WordPress itself and you can find settings under. Settings >> Media.

You can try increasing the thumbnails size.

Screenshot for Clarification: https://ibb.co/6WV5HKJ

After changing the size of the thumbnails you need regenerate the thumbnails using the following plugin: https://wordpress.org/plugins/regenerate-thumbnails/

Best Regards.