function wpc_remove_parent_theme_function() {

    remove_action( 'after_setup_theme', 'extra_add_image_sizes' );
}

function wpc_extra_add_image_sizes() {
    $sizes = array(
        'extra-image-huge'          => array(
            'width'  => 1280,
            'height' => 768,
            'crop'   => true,
        ),
        'extra-image-single-post'   => array(
            'width'  => 1280,
            'height' => 640,
            'crop'   => true,
        ),
        'extra-image-medium'        => array(
            'width'  => 9999,
            'height' => 9999,
            'crop'   => false,
        ),
        'extra-image-small'         => array(
            'width'  => 440,
            'height' => 264,
            'crop'   => true,
        ),
        'extra-image-square-medium' => array(
            'width'  => 440,
            'height' => 440,
            'crop'   => true,
        ),
        'extra-image-square-small'  => array(
            'width'  => 50,
            'height' => 50,
            'crop'   => true,
        ),
        'extra-image-730'   => array(
            'width' => 730,
            'height' => 450,
            'crop' => true,
        ),
        'extra-image-220'   => array(
            'width' => 220,
            'height' => 132,
            'crop' => true,
        ),
        'extra-image-150'   => array(
            'width' => 150,
            'height' => 90,
            'crop' => true,
        ),
    );

    foreach ( $sizes as $name => $size_info ) {
        add_image_size( $name, $size_info['width'], $size_info['height'], $size_info['crop'] );
    }
}

add_action( 'after_setup_theme', 'wpc_remove_parent_theme_function', 0 );
add_action('after_setup_theme' , 'wpc_extra_add_image_sizes');