Most likely there were errors in one of those commands. For me, I had to run
npm install -g @angular-devkit/core first and then run the commands:
npm install -g @angular/cli npm install @angular/cli
In the console output of
npm install @angular/cli you should see:
================================================================================ The Angular CLI configuration format has been changed, and your existing configuration can be updated automatically by running the following command: ng update @angular/cli ================================================================================
Then you obviously should run
ng update @angular/cli to finish off the process.
See the Official Update Guide for additional details.