I first installed npm and made sure it was up to date. Then I tried installing angular but I was faced with errors
~ kode$ sudo npm install -g @angular/cli
You need to delete ng folder from /usr/local/bin
Install again
sudo rm -rf /usr/local/bin/ng
sudo npm i -g angular/cli
I was having the same issue as you but I found that if I went to the /usr/local/bin folder and erased the ng file then reinstalled angular it worked.
If you already tried to install angular follow this the uninstall directions here https://github.com/angular/angular-cli/wiki/stories-1.0-update, then erase the ng file then reinstall.