change portfolio image size

@hoiung: Changes need to be made on child theme as well as you will need to fix the styles which is a bit complicated let me know if you are comfortable with child theme customization in detail. Otherwise I suggest you to hire a customizer.

Kind Regards,
Sapana

@hoiung: Sorry for the late reply, Go to => Child Theme Folder => functions.php and add the code in this link
add_image_size( 'adonis-portfolio', 1200 , 680 );

Go to=> child theme=> Create Template-parts folder=> Create portfolio folder and add the following CSS code

<?php
/**
 * The template used for displaying projects on index view
 *
 * @package Adonis
 */
?>

<article id="portfolio-post-<?php the_ID(); ?>" <?php post_class(); ?>>
	<a title="<?php  the_title_attribute(); ?>" href="<?php the_permalink(); ?>">
		<div class="porfolio-section-thumbnail post-thumbnail">
			<?php
			// Output the featured image.
			if ( has_post_thumbnail() ) {
				$thumbnail = 'adonis-portfolio';

				the_post_thumbnail( $thumbnail );
			} else {
					echo '<img src="' .  trailingslashit( esc_url( get_template_directory_uri() ) ) . 'assets/images/no-thumb-640x480.jpg"/>';
				}
			?>
		</div><!-- .portfolio-content-image -->

		<div class="entry-container caption">
			<header class="entry-header vcenter">
				<?php the_title( '<h2 class="entry-title">', '</h2>' ); ?>
			</header>
		</div><!-- .entry-container -->
	</a>
</article>

Let me know if this works out!

Kind Regards,
Sapana