git remote add upstream git@[server]:[owner]/[remote_repo].git
git fetch upstream && git merge upstream/master && git push
You may be interested in git up http://coderwall.com/p/wdpzgw
I got this alias, which is based on naming conventions.
I usually don't bother updating my fork, I just create a new branch:
git fetch upstream && git checkout upstream/master -b new_featrue
and work from there.