The apache2 version that is installed on Ubuntu is a couple updates behind. This unfortunately exposes your server to unpatched vulnerabilities. This can be fixed easily. So lets get started.
A few quick steps
We will start things off by adding a third party repo.
> sudo add-apt-repository ppa:ondrej/apache2
Now bring everything up to date.
> sudo apt update
> sudo apt dist-upgrade
Not much to it. Enjoy.