if you got BI console open (Web interface will be roughly the same layout which is made in the BI console) click the box with a pencil (marked yellow) which is in the top row, next to the camera group

On the top right of the console.
then, you are in edit mode for this group, you will get a popup which states "
Now right click over any camera to change camera or group layout settings" click the icon again to exit edit mode.
Simply said, right click a camera to change the model of the layout,for example, i got a few portrait mode cameras which are next to each other with landscape next to it to fill the space "big"
And then some smaller cams which i dont look at during the day, but are there just for security measure if theft happens.
In the right click menu you can change all kinds of stuff:
To "move" cameras, just left click and hold the camera, and drag it to the place to kind of "switch" positions for those 2

To make a camera bigger or smaller, right click that specific camera and edit the height (combined with aspect it automatically gives you the width)
If you still can't figure it out give me a quote and i will make a further guide for your layout questions
Happy to help, as the forum has helped me alot too allready