How to Install the Latest Versions of NodeJS For Ubuntu

もっと読む
Use the NodeSource PPA.For details look at the installation instructions.First,chose the Node.js version you need and add the sources for it:

# for Node.js v4
curl -sL https://deb.nodesource.com/setup_4.x | sudo -E bash -
# OR for Node.js v5
curl -sL https://deb.nodesource.com/setup_5.x | sudo -E bash -
# OR for Node.js v6
curl -sL https://deb.nodesource.com/setup_6.x | sudo -E bash -
# OR for Node.js v7
curl -sL https://deb.nodesource.com/setup_7.x | sudo -E bash -

The n install the Node.js package.

sudo apt-get install -y nodejs

P.S.  curl package must be installed on server for these code lines.
Upgrading
If you have  nodejs already installed and want to udate,then first remove current instalation and install it again using scripts above.

sudo apt-get purge nodejs npm