Upgrading Chariot MQTT Server is done via the Chariot Web UI.  The upper right drop-down menu has an option for upgrading.  Upgrades must be applied incrementally. For example you can not upgrade from v1.2.1 to v1.2.3 directly.  You must first upgrade from v1.2.1 to v1.2.2 and then in a separate step upgrade from v1.2.2 to v1.2.3.

• Upgrade from v1.2.1 to v1.2.2
  • https://cirrus-link-public-downloads.s3.amazonaws.com/Chariot+On-Premises/Upgrade_1.2.1_1.2.2/upgrade_1.2.1_to_1.2.2.zip.gpg
• Upgrade from v1.2.2 to v1.2.3
  • https://cirrus-link-public-downloads.s3.amazonaws.com/Chariot+On-Premises/Upgrade_1.2.2_1.2.3/upgrade_1.2.2_to_1.2.3.zip.gpg