private $options_default = array(
		'beta_version' => false,
		'db_version' => 4,
		'convertion_time' => 0
	);

        public function __construct() {
		// init
		add_action( 'init', array( $this, 'options_upgrade' ) );
	}

	function options_upgrade() {
		$options_old = get_option( 'your_plugins_name' );
		if ( $options_old[ 'db_version' ] < $this->options_default[ 'db_version' ] ) {
			$options_old_usable = array_intersect_key( $options_old, $this->options_default );
			$options_new = array_merge( $this->options_default, $options_old_usable );
			$options_new[ 'db_version' ] = $this->options_default[ 'db_version' ];
			update_option( 'your_plugins_name', $options_new );
		}
	}