public function upgrade( $theme, $args = array() ) {

    $defaults    = array(
      'clear_update_cache' => true,
    );
    $parsed_args = wp_parse_args( $args, $defaults );

    $this->init();
    $this->upgrade_strings();

    // Is an update available?
    $current = get_site_transient( 'update_themes' );
    if ( ! isset( $current->response[ $theme ] ) ) {
      $this->skin->before();
      $this->skin->set_result( false );
      $this->skin->error( 'up_to_date' );
      $this->skin->after();
      return false;
    }

    $r = $current->response[ $theme ];

    add_filter( 'upgrader_pre_install', array( $this, 'current_before' ), 10, 2 );
    add_filter( 'upgrader_post_install', array( $this, 'current_after' ), 10, 2 );
    add_filter( 'upgrader_clear_destination', array( $this, 'delete_old_theme' ), 10, 4 );
    if ( $parsed_args['clear_update_cache'] ) {
      // Clear cache so wp_update_themes() knows about the new theme.
      add_action( 'upgrader_process_complete', 'wp_clean_themes_cache', 9, 0 );
    }

    $this->run(
      array(
        'package'           => $r['package'],
        'destination'       => get_theme_root( $theme ),
        'clear_destination' => true,
        'clear_working'     => true,
        'hook_extra'        => array(
          'theme'  => $theme,
          'type'   => 'theme',
          'action' => 'update',
        ),
      )
    );

    remove_action( 'upgrader_process_complete', 'wp_clean_themes_cache', 9 );
    remove_filter( 'upgrader_pre_install', array( $this, 'current_before' ) );
    remove_filter( 'upgrader_post_install', array( $this, 'current_after' ) );
    remove_filter( 'upgrader_clear_destination', array( $this, 'delete_old_theme' ) );

    if ( ! $this->result || is_wp_error( $this->result ) ) {
      return $this->result;
    }

    wp_clean_themes_cache( $parsed_args['clear_update_cache'] );

    return true;
  }