Change the portfolio thumbnail’s size
To change the size of the portfolio thumbnails you’ll need to work with the child theme. As you might have seen already, there’s a list of functions that can be replaced in the child theme. One of those functions is krown_portfolio_thumbnails_size.
If you go in the theme_folder/includes/portfolio-functions.php file, at the bottom you will see that function. Simply copy the contents of the function into the functions.php file of the child theme and replace the values of the arrays with your custom ones.