First I downloaded and unzipped the file from here: https://nodejs.org/dist/v7.4.0/node-v7.4.0-linux-x64.tar.xz
I like to install apps I download into /opt, so:
$ cd /opt
Copied the zip over:
$ sudo cp ~/node-v7.4.0-linux-x64.tar.xz .
Extracted the file:
$ sudo tar xvf node-v7.4.0-linux-x665.tar.xz
Add the bin/node and bin/npm to be in the path by using update-alternatives:
$ sudo update-alternatives --install /usr/bin/node node /opt/node-v7.4.0-linux-x64/bin/node 1
$ sudo update-alternatives --install /usr/bin/npm npm /opt/node-v7.4.0-linux-x64/bin/npm 1
Now I get the expected versions:
$ npm --version
4.0.5
$ node --version
v7.4.0