Hi,

By default WordPress auto create some image sizes, you can check it via Dashboard > Settings > Media.

For image sizes from the theme, you can check it via Appearance > Theme Editor > click on "functions.php" file on the right side > and on line 91, you will see this code:

add_image_size( 'penci-full-thumb', 1170, 99999, false );
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-single-full', 1920, 0, false );
add_image_size( 'penci-thumb', 585, 390, 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 );
add_image_size( 'penci-thumb-small', 263, 175, true );

You can remove any line in all lines above to remove the image size you don't want to create in future uploads.

Best Regards,

PenciDesign