$ sudo n 6.9.1
$ sudo npm -g install npm@next
$ sudo n stable

curl -0 -L https://npmjs.org/install.sh | sudo sh

ncu -g

or　　

npm outdated -g

In linux，when I update to node 7, this happened, "npm cache clean" does work.

In windows, npm cache clean also generate

Error: Cannot find module 'internal/fs'