6.1.5 version of theme is out of date version. So, it could be the reason of the problem. But you did not provide server error logs, so can’t be sure. Anyway, in your case, we would recommend you to create staging site (full copy of the existing site) and provide us with WP Dashboard and FTP access to your staging site. We’ll help you with theme update, you’ll check if everything is ok. If yes then we’ll help you with the production site update.
