Move workstations from 6.9 server to new 7.1 server

I have around 500 machines currently on our DS & NS 6.9 environment, and 200 machines on our new 7.1 environment.

The 6.9 and 7.1 platforms are both on different servers.

What's the best way to migrate the machines from the 6.9 server and point to the 7.1 server?

Do I just push the agent from the 7.1 to the 6.9 machines? will this auto update/re-point the agent?

OR do I need to remove Aclient and Dclient individually, then deploy the 7.1 Management Agent?

Any advice appreciated :) Thanks in advance