Hi,

With your site, here is all images size you can remove:

add_image_size( 'penci-slider-thumb', 1170, 663, true );

add_image_size( 'penci-magazine-slider', 780, 516, true );

add_image_size( 'penci-slider-full-thumb', 1920, 800, true );

add_image_size( 'penci-masonry-thumb', 585, 99999, false );

add_image_size( 'penci-thumb-square', 585, 585, true );
add_image_size( 'penci-thumb-vertical', 480, 650, true );

For all other size, you should keep it.

Also, maybe you need to control more your image sizes via Dashboard > Settings > Media

Best Regards,

PenciDesign