What's the risk in upgrading MySQL and PHP? Could the forum crash?

[Winston]

To anyone who knows anything about webhosting and databases:

In my WHM panel, I get this notification:

Unsupported MySQL Version
This server currently uses a version of MySQL® (5.5) that cPanel, L.L.C., does not support and that will not function in future versions of cPanel & WHM. Update MySQL to ensure that you receive the latest features and security fixes.

To upgrade your MySQL version, use the MySQL/MariaDB Upgrade interface.

When I go to the MYSQL/MariaDB upgrade interface, I see this notification at the top:

After you upgrade MySQL/MariaDB, there is no supported way to downgrade to the previous version.
The table below displays available upgrades and conversions.

Obviously it wants me to upgrade my MySQL version to something above 5.5. But I'm worried because what if my forum crashes when I upgrade it? If that happens, it says that I cannot downgrade to the previous version, as you can see. So my question is: What's the risk? Is it very minimal? I need to know first because the upgrade will be irreversible as you can see.

Do I need to stop all MySQL processes and stop my databases before the upgrade? If so how do I do that? I see no stop button in my phpmyadmin panel.

Also, in the upgrade interface I see many MySQL versions and MariaDB versions. Which one should I pick? Should I just pick the next one above 5.5 which would be 5.6 to be safe? What do you all recommend?

Another question: I cannot upgrade my forum to phpbb 3.3 it seems because my PHP is below 7.1, according to this page about phpbb 3.3:

https://www.phpbb.com/community/viewtop ... &t=2534541

The minimum supported PHP version has been increased to PHP 7.1.3 while support for PHP 7.3 and PHP 7.4 has been added. Fixed security issues in 3.2.9 are part of this release as well.

According to my ACP, my PHP version is 5.6.40. So I'm way below the requirement for phpbb 3.3. So I gotta ask: How do I upgrade my PHP version? And again, what's the risk? Could it crash my forum? If so what are the odds? Are they too small to worry about? Is this process generally safe and risk free?

One more question. On the home page of my WHM panel, I also get this notification at the top:

On November 30, 2020, CentOS will stop supporting CentOS 6 on all systems, including your server. At that time CentOS will no longer provide bug, security, or feature updates. We encourage you to migrate to a server using CentOS 7 before November 30, 2020. Information about cPanel deprecation plan is available in our documentation.

Only system administrators (root and root-level resellers) see this message.

How do I upgrade to CentOS 7? Or migrate my server using CentOS 7? What do I do about that? Any idea?

Thanks for your help.

[HouseMD]

Damn it Winston, I'm a doctor, not a programmer!

[StanfordGuy]

[Winston]

Update:

Ok I just updated MySQL to 5.6 and also PHP to 7.1. There was no 7.1.3, only 7.1. Hopefully that's the same thing.

So far the forum is working fine. It doesn't look like it's caused any problems.

Btw in my PHP panel, I see an option to enable this:

PHP-FPM

Should I turn it on? I asked my webhost and they said it's something that makes PHP scripts run faster. When I googled it, I found this:

PHP FastCGI Process Manager (PHP-FPM) is an alternative FastCGI daemon for PHP that allows a website to handle strenuous loads. PHP-FPM maintains pools (workers that can respond to PHP requests) to accomplish this. PHP-FPM is faster than traditional CGI-based methods, such as SUPHP, for multi-user PHP environments.

Will that make the forum run faster? Is it compatible with phpbb? Is there any risk in turning it on?