If the service update was not committed during installation, then you must commit it after installation once you have decided that you will not be returning to the previous version of the software. Committing the updated version of the service update deletes all previous versions from the system and recovers the disk space that was used to store the previous version. When you are sure that you want to keep the updated version of the software, you should commit it. By freeing up disk space, it is faster and easier to process any new updates you apply at a later date. Before installing a new set of updates, you may want to consider committing any previous updates that have not yet been committed.
If, however, you decide to return to the previous version of the software, you must reject the updated version that was installed. Rejecting a service update deletes the update from the system and returns the system to its former state. A service update can only be rejected if it has not yet been committed. Once committed, there is no way to delete an update except by removing the entire fileset, or by force-installing the fileset back to a previous level (you must have the base level of the fileset available on media to do this).
When you install a base level fileset, it is automatically committed during installation. If you want to delete a fileset, it must be removed (as opposed to rejected) from the system. A fileset is always removed with all of its updates. The Base Operating System (bos.rte) cannot be removed, and certain other products cannot be removed if the software is in use. For example, the devices.scsi.disk fileset cannot be removed from a standalone system with SCSI disk drives, because it controls the disk on the system.
If something should go wrong during the software installation so that the installation is prematurely canceled or interrupted, a cleanup must be run. Detailed information and the procedure for cleaning up software are included in "Cleaning Up Optional Software and Service Updates".
For more information about commit, reject, and remove, refer to "Optional Software Installation and Update Concepts".