Please ensure the below steps to be taken care while upgrading so that the ZD will not lose the configuration. I have also provided the software file links to download.
1. Take the backup of the existing configuration. 2. Upgrade the software on the ZD. 3. Once the ZD is upgraded please wait until the APs upgrade. 4. Ensure that all the APs are connected back to the ZD with the same version before upgrading to the next version. 5. Ensure to take the backup on each version before upgrading to the next version just in case.
Note: Please make sure to check the release notes to understand the supported AP models before upgrading.