The most common method to update your PHP version involves logging into your hosting account and searching for “MultiPHP Manage” via your C-Panel dashboard. If your web host does not use C-Panel as many high-quality WordPress hosts do not, you will want to do a search engine query for how to update PHP on your particular host’s server.

Ex: “how to update PHP on WP Engine” or “Bluehost updating php wordpress.”
In some cases you may need to contact your web host directly and have them perform the php upgrade.