Hello,
To update your PHP version, you must ask your host provider to do so.
This link can help you: https://projectdmc.org/support/update-php/#how-to-update-your-websites-php-version-for-a-faster-more-secure-website
In case you need to know more about PHP version supported by WordPress:
https://make.projectdmc.org/core/handbook/references/php-compatibility-and-wordpress-versions/
The message is generated by a plugin that you are using and that includes and integrates a composer package. Composer as a package platform apparently requires a PHP version that is not available in your hosting.
You have 2 possible solutions:
a) Change your hosting to PHP 8.0 or newer. Today’s recommendation would be to use PHP 8.1, but all the plugins you use and your theme must also be compatible with it (WordPress itself already is). By switching to the PHP version, you should have immediate access again. Contact your hoster’s support team for a solution.
b) Deactivate all plugins via FTP. To do this, log in to your hosting via FTP and rename the /wp-content/plugins directory. Your hoster’s support can tell you how to connect via FTP. You should then be able to log in again and should make sure that you reinstall and activate all of the plugins you are using – except for the problematic plugin, which you can also identify in this way.
