correct image size dimensions

I need the 2020 image size dimensions for this theme. I have seen conflicting specs in various places =theme notations and in the FAQ sections. I need to know what each size is all sections of this theme so I can make my image specific to each. Conflict is apparent in how theme displays my featured images on the page vs the image slider. I want to optimize images. see what I mean at my site; axumcreative.com