There are several versions of the PHP interpreter available: 7.2, 7.3, and 7.4, as well as the deprecated 5.2-7.1. But they are no longer supported by PHP developers and may have vulnerabilities. Use them at your own risk, and only if you have code that doesn’t work with newer versions.
We have a person that is supposed to keep our website up to date with such things but I realised today that he might not and that he has lied to the people before me who has no clue about websites. Wanted to know before I have a discussion with him tomorrow, but generally yes we should have a newer version of PHP?
In general use the latest version you can. Most servers will allow you to change the version you run easily enough.
You can sometimes get errors with the latest version, i.e 7.4, where some PHP code hasn’t been updated (often with 3rd party addons). In cases like that I usually go back and use a previous version, i.e. 7.3 or 7.2 to get things working.
Yes you can swap versions at any time you want, and the change should be instantaneous.
I normally do changes like this out of hours so if there are errors site visitors shouldn’t see them.
So try 7.4, check your public pages and the admin/control panel. If you find errors make a note of them, they can often point to the culprit. If the errors aren’t immediately fixable, try 7.3 and retest, failing that 7.2.