For Zoo 4, you can use these instructions as a guideline:
Zoo 5 is somewhat easier, as all you need to to is remove your licenses and uninstall the Zoo software from the old server, and then install the Zoo software and add your licenses to the new server. Of course, you will need to redirect your clients to use the new server. If you are using DNS, this is just a matter of modifying your DNS alias record. If you are using the Registry, then this will need to be updated on every Rhino system.