Change image size on main featured post – original author response not working

Id like to have a larger featured image and I followed Konstantins (theme author) reply to this question here but there was no change.

“Hey Bill, it’ll be fairly tricky to change the image size, but here’s what you’ll have to do. Firstly, you’ll need to give the main featured content image more space, by default it’s set to 50%, so here’s how you would go up to 100% with some custom CSS:

.featured-content .has-post-thumbnail .entry-thumbnail { width: 100%; }

Then you would need to modify the image size for the large thumbnails, which are registered at 460×260 by default. You can add a new image size in a child theme’s functions.php file, like so:

add_image_size( ‘my-expound-featured’, 560, 360, true );

Finally, you’ll have to make sure the new size is used in your theme, so copy the featured-content.php file to your child theme, open it and find the following piece of code:

the_post_thumbnail( ‘expound-featured’ );

And change expound-featured to my-expound-featured. Note that WordPress will not automatically slice your old images to the new size you have specified, so you’ll have to regenerate thumbnails to see your new size in action.

Learn more about child themes here. Hope that helps!”

Did something change since then that would prevent it from working? Thanks for any help