OK guys, I read (tried on Windows) all the previous stuff and all of these answers have their own disadvantages.
For the best way to update Node.js (at least for me), go to https://nodejs.org/en/
Then download the last version and install it in same folder you installed the previous version in - 1 min and it's done. You don't need to remove any old files.
Then update npm typing in cmd: npm install --save latest-version
