function cac_hero_image_size( $tag ) {
    $tag = preg_replace( '|height="[0-9]+?"|', 'height="325"', $tag );
    $tag = preg_replace( '|width="[0-9]+?"|', 'width="590"', $tag );

    return $tag;
}
add_filter( 'pgw_image_markup', 'cac_hero_image_size' );