Theme Horse

hi got to the functions.php file
there is

	// Add suniltheme custom image sizes
	add_image_size( 'featured', 670, 300, true );
	add_image_size( 'featured-medium', 230, 230, true );
	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
	add_image_size( 'gallery', 474, 342, true ); 				// used to show gallery all images
	add_image_size( 'icon', 80, 80, true );						//used for icon on business layout

for which image size you want. You can change the image size.
Before doing this first unhook the function in child theme and hook the function and change the code.
Hope this may help you
Thank you