Header images loading wrong sized image URL

Hi everyone, I have an issue I can’t solve on my own.
If you view the header images on a website I am a part of. “https://www.thesmokingclutch.com/” You’ll see they are bad quality, this is also the case on profile pages and post pages. I have realised that this is because it is choosing to display a down scaled version of the orginal, as an example, the header image source URL is “https://www.thesmokingclutch.com/wp-content/uploads/2017/11/StephenHodge_StyleCoverOriginal-300×200.jpg” Instead of the full sized version of the image.
Can anyone help me get it to display the original image so that the quality is better?

The page I need help with: [log in to see the link]