Felix Rieseberg of Microsoft has published a great tool which helps updating npm on windows platforms. The repo can be found here
It’s simple to use. Launch an elevated PowerShell, and then:
Set-ExecutionPolicy Unrestricted -Scope CurrentUser -Force
npm install -g npm-windows-upgrade
As the readme of npm-update-windows suggests, make sure to checkout the Microsoft + Node.js Guidelines, if you haven’t already!