1. Open terminal in fork folder
2. Add the original repo calling it “upstream”
git remote add upstream https://github.com/DIRACGrid/DIRACDocs.git

1	git remote add upstream https://github.com/DIRACGrid/DIRACDocs.git

3. Fetch all the branches of that remote
git fetch upstream

1	git fetch upstream

4. Check out your fork’s local master branch.
git checkout master

1	git checkout master

5. Merge the changes from upstream/master into your local master branch. This brings your fork’s master branch into sync with the upstream repository, without losing your local changes.
git merge upstream/master

1	git merge upstream/master

Reference: https://help.github.com/articles/syncing-a-fork/