cPanel
cPanel PHP version: how to plan a version change
A cPanel PHP version selector makes runtime changes easy to click, but the application still has to support the target version. Treat a major PHP change like an application deployment rather than a cosmetic control-panel setting.
Check which domains and applications use the version
Depending on the hosting configuration, different domains can use different PHP versions. Identify the site you are changing and record the current version before editing.
Review required PHP extensions and settings
Applications may depend on extensions, memory limits, upload sizes, execution time, and other settings. A new version with a missing extension can look like a code failure even when the application itself is compatible.
Test dynamic paths after the switch
Check logins, forms, checkout, uploads, image processing, cron jobs, APIs, and administrator tasks. Review PHP error logs rather than judging success from a cached homepage.
Roll back if the application is not ready
Return to the previous supported runtime while you update or replace incompatible software. Avoid solving compatibility by leaving an unsupported PHP version exposed indefinitely.