Drupal 8 is under heavy development, to keep in sync with the latest changes. The easiest and recommended way of updating Drupal Console is using the self-update command.
Depending on the installation method:
Installed globally (and renamed to "drupal"):
$ drupal self-update
Installed globally (using composer):
$ composer global update drupal/console:@stable
Installed locally (running from directory where the console.phar has been downloaded):
$ php console.phar self-update