Hello Stefan,
The Real-time Storage Manager allows to externalize BLOB content based on criteria defined in the rule, upon file upload into SharePoint.
However, to externalize existing content, you will have to configure a rule for Scheduled Storage Manager and run the scheduled manager job, either manual or scheduled.
The SMSP 7.0/7.1 Installation and Administration Guide should be able to walk you through the entire process to configure Scheduled Storage Manager.
Regards,
Cheryl