Pictures not shown in full width (gallery)

Hello dear forum community,
I now also need your help with this excellent theme.
Unfortunately I can’t display the photos in a full width article as described at https://andersnoren.se/themes/hamilton/style-guide/ .
My procedure:
– I create pictures with a width of 1240 pxl.
– upload them to the media center at my backend
– in the article I insert one or two photos as a gallery

Unfortunately the photos are not displayed over the full size like the featured image, but only in a width of 520 pxl.

I’m aware that the topic has already been mentioned here, but I can’t find a working solution for me.

Can you help me?

Thanks
Peter

P.S. my site is currently in maintenance mode.

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