SEPM 12.1.5 Retire old server

So I have OLDSERVER running SEPM 12.1.5 and a local database, and I have NEWSERVER running SEPM 12.1.5 and its own local database.

They are each in their own site, and replication is happening as expected.  50% of the clients are v12, and 50% are v11.  We are finishing the process of getting all clents to v12.

I want to retire OLDSERVER as soon as possible.

What is my process to make sure that all clients will report in to NEWSERVER, and how do I go about properly removing OLDSERVER.

Thanks,

Jeremy