featured image full width

Hi I built a website for work www.creativesigns.uk.com And have the featured images on each page taking up full width. I'm just building a site for a friend and only the home page header fills the full width. I'd like feature image on all pages to fill full width. Not sure what setting I'm missing to make this happen. Can you please advise? Site I'm building is www.ashbeckcaravanservices.co.uk Many thanks for your help. Kind regards Karen