The current WebLogic ASA documentation is from the R12 SP2 version and states the following:
Upgrade from a Previous Release
The SiteMinder Agent for Oracle WebLogic software cannot be upgraded from a
previous version. To install the current version, first uninstall any previous
version of the SiteMinder Agent (or Application Server Agent) for WebLogic. For
more information, see the Agent Guide associated with the release that you must
uninstall.
Applies to SIteMinder WebLogic ASA 12.8
Applies to any OS
Recommended steps to upgrade to 12.8:
As part of WebLogic ASA installation, we only dump binaries in the specified path. The ASA installer does not modify any configuration files of WebLogic itself, so the WebLogic configuration should be preserved.