Directadmin since the version 1.431 allows to have two versions of PHP and a every user on such a server can change a PHP version per domain. And here is a how to find PHP Version Selector from Directadmin.
PHP Version Selector can be found on User Level only.
If you have more than one domain on your account, click the button "Domain Administration" from home page in Directadmin, or click "Domain Setup" link under "Your account" section if you have one domain or on domain's details page.
Click on a domain name for which you want to change a PHP version.
Scroll down the page to see a PHP Version Selector. There you should see a line with "First PHP" and another with "Second PHP". The virst PHP is the very PHP version which will be set for all the files with .php extension. Click and select the desired version and "Save" to confirm changes.
Wait a minute or so to allow changes to take effect and check your site.