npm install npm -g won't update npm to the latest version

Question

I am using npm v5.3.0. Now I want to update npm to v5.4.1.To do this I type the following in my terminal:

npm install -g npm

without any errors.However when I type npm -v the version I get is the 5.3.0 not the 5.4.1

I have to mention that I have changed the npm prefix to another directory. Any ideas? I use Ubuntu 17.04

That's my console output :

Answer 1

I solved it on Ubuntu 18.04 LTS by switching to root using sudo su then I run the following

curl -L https://www.npmjs.com/install.sh | sh