1. To prevent the execution of automatic archiving raise the 'Retention days' of the relevant archive policies at Policies | Backup & Archive/Cleanup.
2. Migrate the logs from the old archive server to the new one.
3. Modify 'Target' and 'Export' according the new archive server at the relevant archive policies.
4. Run an archiving to the new server.
a. Reduce the 'Retention days' at the relevant archive policies.
b. Execute manual archiving by clicking 'Archive/Cleanup ALL' at Log | Logspaces.
5. Check if the archived logs are available at Search | Logspaces.
SSB mounts the new archive share at the start of the archiving, so the archived logs should be available right after the last step.