Hello @ac2017
Thanks for providing the web page link.
By default first box in grid box take “large” image size and all remaining box take “thumbnail” image size as per design preference.
In Lite version there is no way to change it without plugin file change. Below is the plugin file location in case you want to change.
File Location : /wp-content/plugins/blog-designer-pack/templates/grid-box/design-1.php
Line no : 66 – Change the thumbnail parameter to ‘full’.
In Premium version you can modify plugin template by copying its file to your current theme / child theme so you do not have to worry about the plugin update.