Un-blur and un-crop featured Images in the Header

I would like to switch to your theme, Winter Blues, but am not sure how featured images are displayed on individual posts using Winter Blues. Please clarify.

Using the Preview theme option, I see that featured images show in the blog scroll, but when opening any individual post, I noticed the feature image is inserted into the header, cropped, and blurred. How does a user of the Winter Blues theme edit or post featured blog post images without the featured image being automatically blurred and cropped?