Thumbnail Size

Changing thumbnail sizes is easy. To do it, locate where it says “Thumbnail sizes” in functions.php (in the beginning of the code). Here is an example of how it looks:

// Thumbnail sizes
add_image_size( 'themename-small', 160, 160, true );
add_image_size( 'themename-medium', 520, 292, true );
add_image_size( 'themename-large', 1000, 562, true );
		
// Thumbnail sizes custom widgets
add_image_size( 'alx-small', 160, 160, true );
add_image_size( 'alx-medium', 520, 292, true );

Now you need to locate this function, which the image sizes are within:

function themename_setup() { CODE HERE }

Copy the whole themename_setup function to your Child Theme’s functions.php and then go ahead and change the sizes as you wish.

Once you’ve saved the file, you need to go to the WordPress dashboard and run a plugin named “Regenerate Thumbnails“. This will re-crop all images you’ve uploaded to the new sizes.

And… you’re done!