Common WP errors caused after PHP update and how to fix them

OBS: we cannot edit the code of your website for you. If it is needed, you must either do this yourself or find a developer that can help you.

If after upgrading the PHP version, your website stopped working, you may find the following errors:

1. White page with the message "ERROR" - it is most likely to be caused by Joomla being out-of-date, or third-party extensions and/or templates also not compatible with newer PHP versions
2. You see error HTTP ERROR 500.
3. You see the error message: "There has been a critical error on this website." Usually WordPress sends the instructions to your website admin contact. 
4. Some themes and plugins do not support new WP versions and/or PHP versions. You may need to change them in order to have the latest PHP running.

General troubleshooting the following step-by- step can help to solve the issue:

1. Revert the PHP version
2. Update your WordPress installation and plugins
3. Try updating the PHP version again
4. If you still are experiencing any issues, you can enable display_errors in PHP settings, to see the exact error and try fixing it.
5. You can try the WordPress debug_mode

If you are not a web developed or has some knowledge regarding PHP, you may need specialized help.