My website disappeared after updating

Dear Wp.
I built a website six years ago, windowszervizgyor.hu, and now I wanted to update the new template offered by WP, and my page is completely gone, I don’t even see the adim interface: Fatal error: Call to undefined function get_parent_theme_file_path () in / home / window /web/wp-content/themes/new-york-business/functions.php on line 67
What could have happened?

The page I need help with: [log in to see the link]