Adjust Featured Image Size for posts not pages

Im trying to figure out how to adjust the size of the featured images for my Posts only because some of the photos are portrait not landscape. My temporary solution was to just post the image in the body text of the page but the problem with that is that there is then there is no featured image thumbnail photo on the sidebars on other pages where it shows my recent posts. example would be on this page: https://levoov.com/guess-where-i-am/

The theme i am using is elegance 2.6 so if anyone knows how to remove this please let me know.