Hello,
Thank you very much for choosing our theme and for contacting us.
You need to stretch the section and set the background to it: https://gyazo.com/2d3319dd23434ec703e359e68ba7b03e the green is the stretched section, and the blue is boxed content, you need to set the width for the content if you do not want to content also to be full-width: https://gyazo.com/7721f062af195c64d0f73c0fc30de748
If you have any questions please feel free to contact us.
Best Regards
Best Regards