PHP 5.6 had reached "end of life" on January 1st, 2019:
While we still offer PHP 5.6 within cPanel > MutliPHP, we advise all customers to use current version of PHP: 7.2 (as of May 1st, 2020). Please backup all data prior any changes within cPanel or FTP.
How to switch PHP version:
Please login to cPanel then navigate "MultiPHP". There, on the right, you can select version of PHP then your domain name or subdomain name on the bottom. Please hit "apply" button to save changes. Please wait for about 2 minutes then access your website via browser (Google Chtome or Microsoft Edge). If you see 500 error or "internal server error", you should reverse back to PHP 5.6 then upgrade your scripts first. Once you complete script upgrades, you may try to upgrade PHP version again.