How to upgrade PHP version for particular website on server without using cPanel setting. 

Just add the following code in your subdomain's .htaccess file and mention the require php version. <FilesMatch "\.(htm|html|css|js|php)$"> SetHandler application/x-lsphp80 </FilesMatch>

The actual change is made by switching the line with one of these depending on the version look at the last two digits:   SetHandler application/x-lsphp72  SetHandler application/x-lsphp73  SetHandler application/x-lsphp74  SetHandler application/x-lsphp80