I have upgraded my Angular CLI globally but my project is using an older version of angular CLI, so I want to downgrade my Angular CLI globally.
You can downgrade your global angular-cli installation to eg. 1.0.0-beta.14 by issuing:
angular-cli
1.0.0-beta.14
npm uninstall -g angular-cli npm cache clean npm install -g angular-cli@1.0.0-beta.14
The complete upgrade/downgrade guide is on GitHub README.