Upgrading php 7.0 to 7.4

Hi, we have an installation on Ubuntu 16.04 running Matomo version 3.3.0-0 and need to make this upgrade.

Unfortunately we set this up via an AWS AMI and don’t really have a lot of in house Linux experience. I was wondering if anyone who might have been through this process could shed some light on it?

We have installed 7.4, but are unsure what is required to have the Matomo install actually use it.