You already have your remotes configured (see configure remotes), now you want to ensure that your local information related to them is updated with current remote status.
You can fetch the status of bartsimpson remote:
git fetch bartsimpson
or you can fetch all your remotes:
git fetch --all
Fetch does not make any changes to local branches, so you will need to merge a remote branch with a paired local branch to incorporate newly fetch changes.