Lumen 5.5 is now released and available for all. This is considered a maintenance release that upgrades the underlying packages to the Laravel 5.5 series.
Before upgrading your application to Lumen 5.5, you should review the Laravel 5.5 upgrade guide and make any applicable changes to your application according to which Laravel components you are using.
Once you have made the necessary adjustments to your application, you may upgrade your Lumen framework dependency in your composer.json file and run the composer update command:
For more information check out the official Lumen documentation.