GitHub with their web interface makes it really easy to fork a project, but it leaves you alone when it comes to updating your fork with the changes in the original repository. Its actually really easy with a few steps:
git remote add original git://url-to-original-repo
This adds another remote repository. You can use git remote -v to see your existing remotes. There should be “origin” already, pointing to your GitHub fork. You can use whatever name you like for the new remote repository, above I’ve used “original”.
git fetch original
This loads all commits, including branches and tags, from the specified remote repository, using the alias defined above.
git merge original/master
This merges all changes from the original master branch in your current branch, eg. your local master branch.
git push
By default, push pushes everything to your “origin” repository. Which brings your repo up-to-date. That’s it!