git clone [email protected]:YOUR-USERNAME/YOUR-FORKED-REPO.git
cd into/cloned/fork-repo
git remote add upstream git://github.com/ORIGINAL-DEV-USERNAME/REPO-YOU-FORKED-FROM.git
git fetch upstream
git merge upstream/master master
Besides that you can also use git pull which will perform fetch and merge in a single step.
git pull upstream master
4. Now your fork is upto date but locally only not on github. follow bellow procedure to reflect these changes on your github account. Add all files to your git hub fork master branch
git add .
git commit -m "your-commit-message"
6. push all changes to your remote fork repo (reconfirm that your forked repo is your default configured repo under .git directory)
git push