When using Docker, the upgrade is as simple as spinning up a container with the new version. For source installation the procedure is simple as well: The tarball needs to be unpacked, replacing the existing sources. From the archive directory, the file ledgersmb.yaml (or ledgersmb.conf) must be copied. The same needs to be done for any custom CSS theme files in the UI/css directory.
If your setup is using the deprecated ledgersmb.conf INI-style configuration file, you should use the migration utility utils/migration/convert-ini-to-di to generate the new YAML-based configuration format ledgersmb.yaml.