First of all - check your NBU licenses - you need to have NBU Enterprise Server license to enable installation of Media Server.
To add a Media Server you will first of all need another Server license key.
How you proceed depends on the physical connection to the library and tape drives - if SAN attached, the easiest would be to go for SSO where the Master and Media server share the devices and the Master server will be able to do it's own catalog backup directly to tape and still be available to perform restores of the backups that was done by it up to now. It can even still share some of the backup load.
If SCSI attached, you will obviously have to physically connect devices to the new media server. If there are enough tape drives, you might want to keep at least one drive attached to the master for the same reasons mentioned above (no SSO).
If you want to remove device connectivity altogether from the master, you will have to delete the devices and Storage Unit, move all media to Standalone, install the Media Server, connect devices, use the wizard to add them to NBU, add STU, inventory robot, update all policies to go to new STU. Oh, and you will have to add new SERVER entry to all clients to allow backup to different server.
Next step will be change ownership of all media to new media server:
bpmedia -movedb -allvolumes -oldserver <old_server> -newserver <new_server>
If we know what is feasible as far as physical device connectivity goes, we can provide more detailed steps.
