Having posted and had a few problems resolving how to update the agent on remote PCs, it did occur to me, it is possible to just confgure the existing agents to talk to the new server?
The old server is EPO 3.6.1 and is still on - updating the remote PCs.
New server is EPO 4.5 with different name and IP address.
I guess I might have to update the client to 4.0 to work with EPO 4.5 but I assume that could be done once the redirection occurs?
The best (and safest) way to do this is to just push the agent from the new ePO 4.5 server. Once you have this and the agent is reporting to the new server, ePO 4.5 offers the functionality to transfer agents from one server to another. Currently this only works from an ePO 4.5 server to another ePO 4.5 server, but it will be helpful in the future.