WordPress 5.4 has been reminding admins to update PHP to 7.4. Even if you are on PHP 7.1 you will receive the message in your dashboard. Here are the instructions to upgrade from PHP 7.1 Remi Repo on Centos 7.
READ FIRST — IMPORTANT !!!
Get a complete backup snapshot of your server before you complete these update steps
1. First thing you should do is do any core OS updates and package updates.
2. Check which version of PHP you are currently running.
3. Print a list to see all the PHP packages you have installed. You will need to replace all these packages in PHP 7.4. You should copy this list to a file so you can refer to it if you need to. Make a note of the version of PHP here (7x or 7-x).
4. Remove PHP core and all the installed PHP packages.
5. Install the updated remi repository if it is not already installed.
6. Check out a list of all available remi packages (not-required)
7. Disable PHP 7.x and enable PHP 7.4 (Replace x with sub-version of your previously installed version noted above in step 3) and install any extra packages you want / need.
8. Check the updated PHP version.
9. Restart Apache to use the newly installed PHP 7.4