smaller or bigger slider image will be zoomed in or out to fit the slider container, But you can upload a image that has same width and height as your slider so it wont be zoomed in or out,
You can check whats the slider width by checking the "Fixed width" setting in Body tab, by default the width is 1340px, and the slider height is in swiper slider tab, by default the height is 450px
So if you upload a image that is 1340 x 450 it will be perfect
Sorry what widget?