Thanks! The thumbnails image sizes can be changed at functions.php file in the main theme folder. Can you show us your site url so I can understand which thumbnail size you want to change?
You can change the thumbnail image size in Settings > Media > Image sizes > Thumbnail size (screenshot). If you want to make the changes from WordPress options.
Or change them in file functions.php. Read this article for more detailed information: https://support.codeless.co/?ht_kb=ideal-image-size
In the page you have some portfolio items, in grayscale style. So in the functions.php file the line to edit the width/height is: add_image_size( 'port3', 600, 600, true );
The “true” statement is to force the resize to crop the image in the given dimensions. If set to “false”, it will maintain an aspect ratio.
After changing the settings, reset thumbnails (or reupload the images for the changes to take effect on them).
