bundle update

Update the current environment
$ bundle update [GEM] [--local] [--source=SOURCE]


--local: Do not attempt to fetch gems remotely and use the gem cache instead

--source: Update a specific source (and all gems associated with it)

Update will install the newest versions of the gems listed in the Gemfile. Use update when you have changed the Gemfile, or if you want to get the newest possible versions of the gems in the bundle.
Edit this document on GitHub if you caught an error or noticed something was missing.