How to access each disk separately?

I own a MyBook World Edition with 2 disks of 2TB each. I’m using it on Mac, and when I connect to it a see 2 folders: Public and Download.
I realize that the disk is working as RAID, so actually I only can use 2TB. Is a way to access to each disk separately? so I can use the 4TB?
Looking forward to your answer.

If you have it setup as a RAID 1 disk you will have access to 2TB is you have it as a RAID 0 drive you will have access to 4Tb. Check the link below for more information.