So you've cloned somebody's repo from github, but now you want to fork it and contribute back. Never fear!

Technically, when you fork "origin" should be your fork and "upstream" should be the project you forked; however, if you're willing to break this convention then it's easy.

* Off the top of my head *

1. Fork their repo on Github
2. In your local, add a new remote to your fork; then fetch it, and push your changes up to it

    git remote add my-fork git@github...my-fork.git
    git fetch my-fork
    git push my-fork

Otherwise, if you want to follow convention:

1. Fork their repo on Github
2. In your local, rename your origin remote to upstream

    git remote rename origin upstream

3. Add a new origin

    git remote add origin git@github...my-fork

4. Fetch & push

    git fetch origin
    git push origin