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If you initially installed Node.js with Homebrew, run:

brew update

brew upgrade node

npm update -g npm

Or as a one-liner:

brew update && brew upgrade node && npm update -g npm

Note: If you have npm --version < 2.7.1, you should replace update (above) with install.

A convenient way to change versions is to use nvm:

brew install nvm

To install the latest version of Node.js with nvm:

nvm install node

If you installed via a package, then download the latest version from nodejs.org.
See Installing Node.js and updating npm.

Because this seems to be at the top of Google when searching for how to upgrade nodejs on mac I will offer my tip for anyone coming along in the future despite its age.

Upgrading via NPM

You can use the method described by @Mathias above or choose the following simpler method via the terminal.

sudo npm cache clean -f

sudo npm install -g n

sudo n stable

After which you may opt to confirm the upgrade

node -v

Your nodejs should have upgraded to the latest version. If you wish to upgrade to a specific one say v0.8.19 then instead of

sudo n stable

use

sudo n 0.8.19

EDIT
Avoid using sudo unless you need to. Refer to comment by Steve in the comments

Go to http://nodejs.org and download and run the installer.
It works now - for me at least.

You could install nvm and have multiple versions of Node.js installed.

curl https://raw.github.com/creationix/nvm/master/install.sh | sh

source ~/.nvm/nvm.sh

and then run:

nvm install 0.8.22  #(or whatever version of Node.js you want)

you can see what versions you have installed with :

nvm list

and you can change between versions with:

nvm use 0.8.22

The great thing about using NVM is that you can test different versions alongside one another. If different apps require different versions of Node.js, you can run them both.

I use Node version manager (called n) for it.

npm install -g n

then

n latest

OR

n stable

Simply go to node JS Website and install the latest version.

Do install latest version instead of the recommended stable version. It will give you freedom to use latest ES6 Features on node.

Can be Found here Node JS.

also to update npm, you will have to use this command.

sudo npm i -g npm@latest

All your projects will work fine.

Other option for mac :: brew update && brew install node && npm -g npm

On macOS the homebrew recommended way is to run

brew install node

npm install -g npm@latest

I am able to upgrade the node using following command

nvm install node --reinstall-packages-from=node

sadly, n doesn't worked for me. I use node version manager or nvm and it works like a charm. heres the link on how to install nvm: https://github.com/creationix/nvm#installation

• 
  nvm i 8.11.2 upgrade to latest LTS


• 
  nvm use 8.11.2 use it


• 
  node -v check your latest version

Go to the website nodejs.org and download the latest pkg then install.
it works for me

I used brew to upgrade my node. It has installed but it located in /usr/local/Cellar/node/5.5.0 and there is a default node in /usr/local/bin/node which bothers me. I don't want to make soft link because I don't really know how brew is organized.
So I download the pkg file, installed and I got this info:

Node.js was installed at

/usr/local/bin/node

npm was installed at

/usr/local/bin/npm

Make sure that /usr/local/bin is in your $PATH.

Now the upgrade is completed

You can just go to nodejs.org and download the newest package. It will update appropriately for you. NPM will be updated as well.

You can run but you can't hide... At the end you will be using NVM anyways.

I think the simplest way to use the newest version of Node.js is to get the newest Node.js pkg file in the website https://nodejs.org/en/download/current/
if you want to use different version of Node.js you can use nvm or n to manage it.

sudo npm install -g n

and then

sudo n latest for linux/mac users

For Windows please reinstall node.

Nvm
Nvm is a script-based node version manager. You can install it easily with a curl and bash one-liner as described in the documentation. It's also available on Homebrew.

Assuming you have successfully installed nvm. The following will install the latest version of node.

 nvm install node --reinstall-packages-from=node

The last option installs all global npm packages over to your new version. This way packages like mocha and node-inspector keep working.

N
N is an npm-based node version manager. You can install it by installing first some version of node and then running npm install -g n.

Assuming you have successfully installed n. The following will install the latest version of node.

sudo n latest

Homebrew
Homebrew is one of the two popular package managers for Mac. Assuming you have previously installed node with brew install node. You can get up-to-date with formulae and upgrade to the latest Node.js version with the following.

1 brew update

2 brew upgrade node

MacPorts
MacPorts is the another package manager for Mac. The following will update the local ports tree to get access to updated versions. Then it will install the latest version of Node.js. This works even if you have previous version of the package installed.

1 sudo port selfupdate

2 sudo port install nodejs-devel

Use nvm to upgrade node as per the project requirement..

install nvm through homebrew..
brew update
brew install nvm
mkdir ~/.nvm
nano ~/.bash_profile

In your .bash_profile file (you may be using an other file, according to your shell), add the following :

export NVM_DIR=~/.nvm
source $(brew --prefix nvm)/nvm.sh

source ~/.bash_profile
echo $NVM_DIR

These 2 methods I tried are not working:

1. Use npm

sudo npm cache clean -f

sudo npm install -g n

sudo n stable

2. Manual install node from official website (https://nodejs.org/en/)

After trying, node -v still shows the old version of node.

Below method works for me:

Step 1: Install nvm (for more details: https://github.com/creationix/nvm#installation)

Open terminal and type this command:

curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.33.11/install.sh | bash

Close terminal and reopen it.

Type this command to check if nvm is installed:

command -v nvm

Step 2: To download, compile, and install the latest release of node, type this:

nvm install node ("node" is an alias for the latest version)

To check if node gets the latest version (v10.11.0).

Installing the latest node also installs the latest npm.

Check if npm gets the latest version (6.4.1).

for latest release:
nvm install node

specific version:
nvm install 6.14.4

https://github.com/creationix/nvm

I had the same problem. This is what worked for me because I downloaded and installed node.js globally from the node.js website.

What I did was Give NVM (Node Version Manager) a try. Please do the commands in the following order in your terminal

1. curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.33.11/install.sh | bash




2. command -v nvm




3. nvm install node




4. node -v (to confirm the update)

I was able to update in ~20 seconds with just one line of code

sudo n latest

Other commands weren't working for me, but this one worked. Hope it helps somebody.