Updating the application is very simple, thanks to the use of composer.
cd path/to/your/directory composer update
Composer allow to control strictly the versions to be used in the application. This allow to manage a production server, a staging one and a developpement one.
For the production one, define very precisely the versions of each component in the composer.json file at the root of the application and require only stable versions. In this situation even if an update of composer is launched, the sources will not be modified.
For the staging and development one, let open choices to the versions or accept development versions and using composer update will automatically update the selected modules. Once validated at staging level they can be sent in production re-precising the latest accepted versions.
It is advisable to keep the version of composer up to date. To do that, just launch the following command in a terminal.
If this update create troubles (which doesn’t happen often) you can always undo this update running:
composer self-update --rollback
See the the composer documentation for all details.