This is the situation where you fork the original repository and now want to update your fork to reflect all the new commits and changes present in the original

You will need to add the remote origin as a available

git remote -v

This will list your current remotes which will look like this likely

origin  https://github.com/Siliconrob/ServiceStack (fetch)
origin  https://github.com/Siliconrob/ServiceStack (push)

Now use this command to add the original repository as valid remotes

git remote add upstream https://github.com/ServiceStack/ServiceStack.git

List the remotes again

git remote -v

You should have this now

origin  https://github.com/Siliconrob/ServiceStack (fetch)
origin  https://github.com/Siliconrob/ServiceStack (push)
upstream        https://github.com/ServiceStack/ServiceStack.git (fetch)
upstream        https://github.com/ServiceStack/ServiceStack.git (push)

Now fetch the new remotes latest

git fetch upstream

Make sure you are checking out your forks master branch

git checkout master

Merge the fetched remote into your master branch fork

git merge upstream/master

Now commit the changes and push to your fork and you will have reset your forked repository to match the commit logs and changes of the original