Can you please share the WP admin login details of your site, I have just disabled the plugins folder from the FTP and now the site is back but I have to check the issue from the WP backend. I think you have not updated the WP version before the theme update.
Your issue has been solved. The SamedayCourier Shipping plugin is created the issue on your site. It is not compatible with the latest WP version. Please contact the plugin author support about this issue and ask them compatible the plugin with the latest WP version.