First of all: create a backup of the entire project. You can do this via your host or with the help of one of the backup plugins: https://wordpress.org/plugins/tags/backup/
Then you can choose one of the following options:
a) Make a copy of the project and test the upgrade of all components there. This plugin can help you with this: https://wordpress.org/plugins/wp-staging/
b) Perform the upgrade directly on the live system. If anything goes wrong, you will have the backup.
Before updating, check the PHP version you are using. If it is 7.4 or newer, you are on the safe side as far as the update is concerned, but you should definitely switch to 8.1 or newer at the end of the upgrade, as older versions of PHP will no longer receive any updates. Your host’s support team can tell you how to set the PHP version.
To install the updates, I would recommend updating WordPress itself first, then the plugins, and then the theme. This shouldn’t take long overall, but it also depends on the number of plugins and the structure of the project.
After installing the updates, check whether you still have components (plugins or themes) for which there are no more updates. You will then have to decide what to do with them: delete them, replace them, or (potentially dangerous) continue using them.
And always remember to make backups 🙂
Thank you very much for the advice!
What I would also like to know is whether there is a high probability that the site could break when switching from such an outdated version to a much more advanced one.
That depends very much on the plugins and themes you use. As described above, you should check whether there are updates for all of them. It is also possible that there are plugins that are not compatible with newer PHP versions. The current version of WordPress is compatible with PHP 8.3, with PHP 8.4 only designated as “beta support” and, in my experience, not causing any problems. But plugins and themes are the sticking point. Always create backups as described above so that you can revert at any time. If you have questions about individual plugins and themes, please refer to their support forums.
