This might help someone. Neither "npm-windows-upgrade" nor the installer alone did it for me. Powershell was still using an older version of node and npm.
So this is what I did (worked for me):
1. Download the latest installer from nodejs.org. Install node. It will update your node; everywhere (Powershell, cmd etc.).
2. Install the npm-windows-upgrade package (npm install -g npm-windows-upgrade) and run npm-windows-upgrade.
I didn't uninstall anything and didn't set any paths.
