how to update a git fork

open up your terminal
if you haven't already, clone the repository by doing git clone [url].git where [url] is the address of the repository. if you use github and feel lazy the clone/download button will have the .git address you need with a convenient copy button.
cd into the project's folder
git fetch upstream (if you receive an error, you may need to try this guide)
git checkout master
git merge upstream/master
git push origin master