Node Version Manager is a "POSIX-compliant bash script to manage multiple active node.js versions." It is a very useful tool for taming Node.js which can throw up some strange problems when you install it in the standard fashion.
However I only ever use two commands, which I can never remember off the top of my head, so here they are:
nvm install --lts
I only realised this was an option recently thanks to a post by MuffinMan.
And to confirm which versions you are using:
node --version && npm --version