Change the PHP versionAnd the most important PHP settings

Published on October 20, 2026

Why the PHP version matters

PHP is the language in which WordPress, Joomla, TYPO3 and most shop systems are written. The version in use decides three things:

• Security. At some point, older PHP versions no longer get security updates. A site on an expired version is permanently vulnerable, no matter how up to date the CMS on top of it is.
• Speed. There are significant performance jumps between PHP generations. A version change is often the cheapest performance improvement of all - without changing a single line of code.
• Compatibility. Current CMS versions require a minimum version. Conversely, older plugins sometimes only run up to a certain version.

All current PHP versions are available to you on the web hosting, and you choose them per domain - so an older site can keep running while your new project runs next to it on the latest version.

Before switching: check compatibility

A version jump is done in seconds, but it can bring a poorly maintained site down immediately. Three preparation steps:

1. Take a backup. Via the backup manager in Plesk, including the database. See Create and restore backups.
2. Update the CMS, themes and plugins. Most compatibility problems disappear through that alone.
3. Test on a copy. If you use WordPress, clone the site via the WordPress Toolkit to a subdomain and switch there first. Only once the copy runs cleanly do you follow on the live site. If the copy fails with a white page, narrow down the cause following the approach in Fix WordPress errors.

Switching in Plesk

1. Open the domain in question in Plesk.
2. Go to PHP Settings.
3. Choose the desired version in the PHP version selection field.
4. Save - the change takes effect immediately.

The setting applies to one domain or subdomain at a time. If you run several projects on one web hosting plan, you have to make the switch for each of them individually.

Afterwards: check the site specifically

After switching, do not only open the home page. Errors usually show up elsewhere:

• Backend login and admin area
• Contact and order forms
• Pages with extensions such as sliders, maps or calendars
• The checkout process, if you run a shop

If a page stays white, it is almost always a PHP error in a plugin. In that case, set the previous version back - the site is immediately reachable again - and look for the cause calmly.

The relevant PHP settings

In the same dialog, further values can be adjusted that are frequently needed in practice:

• memory_limit: how much memory a PHP script may use. Set too low, the import of large content or a page builder aborts in the middle of the process.
• upload_max_filesize and post_max_size: the maximum size of an upload. Relevant when importing databases or large media libraries. Depending on the plan, 10 to 100 MB are possible - both values must match each other; post_max_size should be at least as large as upload_max_filesize.
• max_execution_time: how long a script may run. If it is too tight, long-running imports fail - and so do longer cron jobs.
• display_errors: leave it switched off on a live site. Otherwise, error messages reveal paths and versions that nobody outside needs to see.

Which version should I choose?

As a rule of thumb: the newest version your CMS officially supports - not necessarily the very newest one available. Directly after a new PHP generation is released, plugins often still lag behind.

For a new installation, choose the latest version offered. For an existing site, follow your CMS's recommendation and work your way up in steps instead of skipping several generations at once. If the site is slow, the PHP version is only one lever - more in Speed up your website.

Frequently asked questions