Image resizing problem

I’m trying to make the images in my posts bigger but with no luck so far.
For example in this post http://aladyofleisure.com/arch-hotel-london/ I’d like the first image to go across the whole screen.
The second image sticks out further so I don’t think it’s a margins issue.
In Settings-Media the large image sizes are 2024 width and height so I don’t think it’s that.
When editing the picture in Image Detail the full size image settings are 692 x 421 but it’s not coming out that big (snaps back to something like 474).
So I checked my CSS and it says

.post-navigation,
.image-navigation {
margin: 24px auto 48px;
max-width: 474px;
padding: 0 10px;

I tried changing all those one by one but no difference to the image size.

In my CSS there doesn’t seem to be a restriction on image size (ie max-width are all set to 100 pc)

I just want to be able to drag the image to be wider but it always snaps back.

I’m using the 2014 theme and have installed Jetpack and Simple Image plugins but they haven’t made a difference so far.
Previously asked questions all seem to suggest changing Settings-Media sizes but I’ve done that and no change.

Many thanks in advance if someone can help!