Featured Image (zoom and cropped)

I updated to Switty today and love the flexibilty.

I am having issues that seem similar to other topics but I have not found a solution in my particular instance.

What are the preferred dimensions for images displayed as featured images (posts and pages)and header images when y=using the Switty theme?

I have modified the theme-setup.php page and it does not affect the display.

The featured image on the following page appears as I want it to, but has perhaps “inherited” it’s sizing from a previous theme. I am afraid if I change the image as I have on the main page, it will also be zoomed and cropped. That featured image can be viewed on this page:
https://www.theloudwater.com/lost_dog/

This is easily the best theme I have used so far and I very much appreciate the time in your response.

Thank you,

Paul

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