If the update can not be completed, or if you need to restore the pre-update version of the system, the application and database backups can be used to restore the system to the pre-update status.
In some cases, it may be more expedient to address post update issues by correcting them in the current build. Any required change should be isolated if the customer is converting to the currently released version. Any modifications to the build are tested using the normal software testing and release cycle and the update is installed once the fix has been released. This option makes sense when the update is needed onsite and the fix is relatively minor, or when the turnaround time to solve the problem is less than the time required to restore the prior version.