The slider is resized correctly, on mobile devices the size is correct, if you want a bigger slider you can have it bigger by adding higher images ( like 1600x1400px image sizes for example ) or you can remove the padding from the container with this Custom CSS:
padding-left: 0 !important;
padding-right: 0 !important;
padding-bottom: 0 !important;
width: 100% !important;
height: auto !important;
Please add the above CSS to your Child Theme’s style.css or in case you haven’t setup a Child Theme already, then you can also add the CSS to wp-admin -> Appearance -> Customizer -> Additional CSS so you won’t loose the changes after Theme or WordPress updates.
Please let me know how it works.