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'nvm' is used to manage the versions of Node.js installed on your computer. Using it, you can upgrade and change which version you're running. If you want to install a different version of `nvm` you can replace the `v0.39.1` with whatever version you'd like to use. Alternatively, you need to use `wget` to install nvm` on Linux or Mac. Using nvm on Windows you'll need to install an 'nv-windows' package like nvm-windows.