Commands to keep a fork in sync with the upstream repo.
To keep it up to date with the original source repo (the one you forked it from):
git remote add $yourLocalNameForTheUpstream $URLForTheUpstreamRepo
To check you set the remote repo as the upstream for your fork:
git remote -v
To check which branch you are working on locally:
git status
Pull changes from the upstream branch:
git pull $yourLocalNameForTheUpstream $localBranchName
If you accidentally specify the incorrect URL for the remote upstream you forked you can change it by doing the following (as seen when using git remote -v):
git remote set-url $yourLocalNameForTheUpstream $correctURLForTheUpstreamRepo
At this point you have pulled all changes from the remote upstream repo locally to your machine. You then need to push these changes to your remote fork on github:
git push