[Theme Horse Support Team]

hi chantal.attia,

Yes you are using the narrow layout. Its the default layout of the theme. Go to theme folder -> functions.php on line no 143 and you will find this code.
add_image_size( 'slider-narrow', 1038, 460, true );

Replace this code with larger size you want.
add_image_size( 'slider-narrow', 1220, 460, true ); // where 1220 is width and 460 is height of slider

Then install regenerate thumbnails plugins in your dashboard. https://wordpress.org/plugins/regenerate-thumbnails/

Then now your image will show in 1220 and 460

But 1 thing remember while updating to new version your need to change the same code again. Because all your customized code will be lost while updating to new version. So better make child theme and then customize the code.

Thank you!