CI says I need PHP 8.1

Hello
You should be able to change the PHP version according to the requirements indicated

You are without instructions to change the PHP version on a hosting with cPanel

These are other instructions for a normal hosting
Generally the instructions are similar between one hosting and another
It is important to delete the cache to review
It is also advisable to review the results in an incognito window, with different versions of PHP, one by one.
For security reasons it is important to keep the latest versions of PHP running on all applications