Resize images in Wordpress Theme to 100% instead of Fixed Width

Hello, Images in the wordpress theme I purchased are being resized to 1100px (give or take - a 4:3 ratio) and when I have panoramas, they are heinously cropped on the left and right. This only affects the images uploaded using the FEATURED IMAGE and affect FEATURED IMAGES when displayed on both HOME PAGE and on SINGLE PAGES. I need the FEATURED IMAGE engine to display my photos, otherwise I'd use a workaround. So FEATURED IMAGE width needs to be changed, but I need help on how to do it. Therefore, I need you to look into the stylesheet to figure out what is making these images be resized both on the home page and single posts pages. When I give you the examples you'll see that I have two images in the posts, the FIRST IMAGE is displayed right under the post title (featured image inserted automatically pulled from featured image upload), and a second image will be posted under the blog post contents (inserted image manually by me uploaded into the post). My wish is to allow the automated FEATURED IMAGE to lead both on the HOME PAGE and on SINGLE POST PAGES near the top, right where it is, no need to move anything around, and secondly to delete any other instances of the image below (which I can do). All you need to do essentially is find where and why these FEATURED IMAGES INSTANCES are being resized to a particular size resulting in the cropping. **My website is currently in maintenance mode, but I will give the winning freelancer admin access. Until then you can see a screenshot of the site and what I'm talking about: