I used the following instructions to upgrade from NodeJS version 0.10.6 to 0.10.21 on a Mac.
1) Clear NPM's cache:
sudo npm cache clean -f
2) Install a little helper called 'n'
sudo npm install -g n
3) Install latest stable NodeJS version
sudo n stable
Alternatively pick a specific version and install like this:
sudo n 0.8.20
For production environments you might want to pay attention to version numbering and be picky about odd/even numbers.
General procedure: D.Walsh
Stable/unstable versions: P.Teixeira