Alpine Linux PHP7 to PHP8 upgrade

I run a web server on Alpine Linux. Previously I used PHP7, and I wanted to upgrade to PHP8. What is the proper way to do this? I tried with apk del php7 and then apk add php8, but it looks like this does not work properly: a simple PHP test page with just ` displays the right php version, but is missing the proper formatting. Under /var/log/apache2/error.log` I don't see php related errors, though.