On Windows download latest "Windows Installer (.msi)" from http://nodejs.org/download/ and install same directory , thats all...
After complete the installation above, the NodeJS and NPM will be upgraded to the latest one and then you can cleanup the package as normal as:
npm cache clean npm update -g
You can always check the version with following command:
C:\node -v v0.12.4 C:\npm -version 2.10.1