For anyone who comes here, as I did, looking for the syntax to change origin to a different location you can find that documentation here: https://help.github.com/articles/changing-a-remote-s-url/. Using git remote add
to do this will result in "fatal: remote origin already exists."
Nutshell:
git remote set-url origin https://github.com/username/repo
(The marked answer is correct, I'm just hoping to help anyone as lost as I was... haha)