1. Stop archiving to the old server
Raise the 'Retention days' of the archive policies using the old server as target at Policies | Backup & Archive/Cleanup
2. Copy or move the logs from the old share to the new share.
Double-check if all the logs are correctly migrated to the new server.
3. Run an archiving to the new server.
a. Reduce the 'Retention days' of the relevant archive policies.
b. Execute manual archiving by clicking 'Archive/Cleanup ALL' at Log | Logspaces.
4. 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.