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Hi Ron,
You should do an in-place upgrade since it's a single server. The Swing migration will need at least two servers - one active server and one staging server. The normal synchronization will stop during upgrade, so the connection will lost temporarily. After finish, normal delta synchronization will start again.
For more details about AAD Connect Automatic upgrade, you can referring to the following article: https://docs.microsoft.com/en-us/azure/active-directory/hybrid/how-to-connect-install-automatic-upgrade. Automatic upgrade is not supported when you are not using a SQL Server Express LocalDB database.
I hope the above information helps.
Best Regards,
Shawn