To change the PHP version of your website, go to the Websites section and click on Manage next to the website in question. Then, search for PHP Configuration on the sidebar and click on the given result to access those settings:
On the PHP Configuration page, select the PHP version you wish to use and click on Update:
The PHP version will be updated within a couple of minutes.
How to Select an Unsupported PHP Version
To enhance website security and protection, make sure that your website code is compatible with the latest PHP version.
However, sometimes an older PHP version may be necessary, e.g., for testing and troubleshooting. To find all the available versions, click on Show no longer supported PHP versions:
Make sure to revert it back to a supported version once you're ready.