[Theme Horse Support Team]

Hi chantal.attia,

Could you provide your site Url too? Do you mean to change the slider image size? Which layout are you using? Narrow layout or wide Layout?
This is the below slider image size.

add_image_size( 'slider-narrow', 1038, 460, true ); 		// used on Featured Slider on Homepage Header for narrow layout
	add_image_size( 'slider-wide', 1400, 460, true ); 			// used on Featured Slider on Homepage Header for wide layout

If you want to change it then go to theme folder -> functions.php on line no 143 and 144 and you may change the slider size. After changing the slider size then you need to install regenerate thumbnails to re generate the image size.
https://wordpress.org/plugins/regenerate-thumbnails/

But we recommended you to create a child theme and then only customize the code so that while updating to new version your customized code will be lost and you need to do the same things again. If you are unable to fix it then you need to hire a developer to fix it.

Thank you!