change default image size

Hi,

How do I change the default image size for image uploads to the media library?

By default, it seems like the theme uploads images in a 570 x 350px resolution.

I would like to change this to a different value. How do I do this?

I already tried using the media settings, but the theme still uploads in the default resolution. I also tried WP Smush, but it doesn’t do anything.

Thanks.