Clients use the versioning system of their underlying operating system, and require regular upgrades.
For SCC registered clients using SUSE operating systems, you can perform upgrades within the Uyuni Web UI. For supported SUSE Linux Enterprise 15 upgrade paths, see https://documentation.suse.com/sles/15-SP3/html/SLES-all/cha-upgrade-paths.html
To upgrade clients running SLE 12 to SLE 15, the upgrade is automated, but you need to do some preparation steps before you begin. For more information, see Client - Major Version Upgrade.
You can also automate client upgrades using the content lifecycle manager. For more information, see Upgrade Using the Content Lifecycle Manager.
For more information about product migration such as service pack upgrades openSUSE Leap minor version upgrades, or openSUSE Leap to SUSE Linux Enterprise migrations, see Product Migration.
For more information about upgrading unregistered openSUSE Leap clients, see Upgrade Uyuni Clients.