Essentially you'd need to reverse the steps in install.sh - remove any nvm lines from ~/.bash_profile (and/or ~/.profile), rm -rf ~/.nvm, and either reopen your shell, or re-source your bash profile.
However, simply removing the nvm commands from your .bash_profile or .profile should be more than sufficient.
someone else said this:
rm -rf ~/.nvm
rm -rf ~/.npm
rm -rf ~/.bower