Have a look / read through the following articles:
Generally speaking, do one step at the time; try a migration from one server to another server by using the same BE version and perform the upgrade of BE either before or after the migration or if required, before and after the migration.
How to migrate Backup Exec to another server with a different Windows OS version
https://www.veritas.com/content/support/en_US/article.100001807
How to Copy the Backup Exec Database (BEDB) from an existing Backup Exec Server to a new Media Server with the same or different server name
https://www.veritas.com/content/support/en_US/article.100017867
How to migrate (move) Backup Exec from one computer to another using the same version of Backup Exec and Windows, and the same computer name.
https://www.veritas.com/content/support/en_US/article.100012412
