It's no different than upgrading any other Firepower service module.
https://www.cisco.com/c/en/us/td/docs/security/firepower/630/asa-fp-services/asafps-local-mgmt-config-guide-v63/updating_asa_firepower_module_software.html#con_7775954
From Configuration > ASA FirePOWER Configuration > Updates, choose the new release that you have downloaded and upgrade to it. Be sure to read the release notes to make sure you're following a supported upgrade path.
This assumes the Firepower service module is locally managed (i.e. via ASDM). I would generally expect an enterprise level firewall like an ASA would be managed by Firepower Management Center (FMC). If so, it will show under the Firepower tab of the ASDM homepage as having a managing "DC" (Defense Center = old name for FMC). In that case you would perform the upgrades from the FMC GUI under System > Updates.
