MyBook Studio II not seeing full capacity of drives

I have a MyBook Studio II that came with dual 500GB drives.  I bought two replacement 2TB WD Green drives (WD20EARS), but it still only sees a capacity of 500GB.  How do I fix this?  I looked all over the WD site before buying the drives, and these were listed as compatible, and there was nothing that said you couldn’t switch to larger drives.