Normally, you won't install multiple versions of Node.js and doing so adds complexity to your system. But if you are hacking on Node.js itself, or are testing your software against different Node.js releases, you may want to have multiple Node.js installations. The method to do so is a simple variation on what we've already discussed.
Earlier, while discussing building Node.js from source, we noted that one can install multiple Node.js instances in separate directories. It's only necessary to build from source if you need a customized Node.js build, and most folks will be satisfied with pre-built Node.js binaries. They, too, can be installed into separate directories.
To switch between Node.js versions is simply a matter of changing the PATH variable (on POSIX systems), as follows, using the directory where you installed...