Until you click on the "Finalize" button on the ambari during the upgrade the Upgrade is not considered as completed.
When the rolling upgrade stages complete, may choose to Finalize the upgrade, to Finalize Later or to Downgrade. Finalizing later gives you a chance to perform more validation on the cluster. Downgrade moves the cluster version back to the previous version (basically: reverses the upgrade process stages). Once finalized, you cannot downgrade back to the previous version.
Note : If you choose to finalize later, both versions will be listed on the Stack and Versions tab with the starting version displaying as Current. It is not until you finalize that Ambari makes the target version the current version. Also, until you finalize, you will not be able to perform operational changes to the cluster (such as move components, change configurations, etc).
You can get more detailed information about "Rolling Upgrade" and "Express Upgrade" options here: