Syncing a fork

To sync a fork with the origin, you should set upstream remote origin.
And the you can sync a fork as below.

git fetch upstream
remote: Counting objects: 75, done.
remote: Compressing objects: 100% (53/53), done.
remote: Total 62 (delta 27), reused 44 (delta 9)
Unpacking objects: 100% (62/62), done.
From https://github.com/ORIGINAL_OWNER/ORIGINAL_REPOSITORY
 * [new branch]      master     -> upstream/master

git checkout master
Switched to branch 'master'

git merge upstream/master
Updating a422352..5fdff0f
Fast-forward
 README                    |    9 -------
 README.md                 |    7 ++++++
 2 files changed, 7 insertions(+), 9 deletions(-)
 delete mode 100644 README
 create mode 100644 README.md

git merge upstream/master
Updating 34e91da..16c56ad
Fast-forward
 README.md                 |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

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