https://nodejs.org/en/download/package-manager/

The code below will install Nodejs 8 (LTS)

$ sudo curl -sL https://deb.nodesource.com/setup_8.x | sudo -E bash -
$ sudo apt-get install -y nodejs

Alternatively, for Node.js 9:

$ curl -sL https://deb.nodesource.com/setup_9.x | sudo -E bash -
$ sudo apt-get install -y nodejs

Optional: install build tools

To compile and install native addons from npm you may also need to install build tools:

$ sudo apt-get install -y build-essential

How to remove Nodejs

https://askubuntu.com/questions/786015/how-to-remove-nodejs-from-ubuntu-16-04

This will remove Nodejs and npm:

$ sudo apt-get purge nodejs
$ sudo apt-get autoremove

RESOURCES

https://www.digitalocean.com/community/tutorials/how-to-install-node-js-on-ubuntu-16-04