Hello Alessandro,
Good Day!
The upgrade process for ZD's in SR is an automated one, all you need to do is initiate the upgrade on the PRIMARY ZD, once the upgrade is initiated, the SECONDARY ZD is actually upgraded first, all the AP's failover to the Secondary ZD and this ZD will become the ACTIVE ZD. Post this the ZD on which you initiated the upgrade will go through the upgrade process and assume the role of the STAND-BY ZD.
Hope this has answered your query.
- Bittu
