The Downgrade releases option appears only when the downgraded deliveries feature is enabled in your Windchill installation.

The Downgrade releases option provides you the flexibility to select the releases for which you wish to create the downgraded deliveries. The downgraded ZIP files are available as attachments to the corresponding downgraded deliveries in the Deliveries table. The number of downgraded deliveries created depends on the number of releases that you selected.

You can opt not to select any release. In such a case, no downgraded delivery is created.