Ubuntu doesn't ship with the newest version of ansible out of the box, sadly. You have to manually configure the PPA on your system in order to upgrade to the stable version. Follow these commands to install the PPA:
$ sudo apt update
$ sudo apt upgrade
$ sudo apt install software-properties-common
$ sudo apt-add-repository ppa:ansible/ansible
Hit Enter when asked, and once the process is done update your apt repos:
$ sudo apt update
Now you can either upgrade or simply install ansible:
$ sudo apt install ansible
This should be all, use the following to verify the ansible version:
$ ansible --version