6.3 and higher will only work on 64-bit OS.
So for Netsight or Extreme Management Center Server, 6.2 is the last 32-bit supported OS.
Going higher will require moving to a 64-bit OS. Back up the 6.2 Database, and then deploy 6.2 on a64-bit OS and import it.How to backup a Netsight Database using ConsoleHow To Backup, Restore, and Schedule a backup of the NetSight Extreme Control Center Database
NAC devices configuration are generally stored on the Netsight server, except if running DNS proxy. Best to run and capture a 'nacstatus' before upgrading them via ISO or new .OVA deployment.