Updating the mirror to get the latest updates is easy, just run:
git pull && npm install
This will sync the remote changes from whatever branch you are on (most likely
master) to your local machine. This will also install/update any new or updated dependencies.
Sometimes new dependencies are added to the mirror or old ones are updated. In this case you need to update/install them:
npm updatenpm install
Occasionally there can be strange issues with the changes in dependencies. In this case the easiest thing to do would be to clean your repository. This will remove all uncommitted changes (except for your config file) and re-install all dependencies:
git clean -xdf -e config.jsonnpm install