Delete all and/or format to reset?

Hello all, I used a 8TB My Book Live Duo Personal Cloud Storage Network to backup my video business for 2015. I used under 4GB and have it setup to backup to both drives for redundancy. I just purchased a 4GB My Book so I can backup the 4GB from my Live Duo to this new drive, then reuse the Live Duo for 2016. Can I simply delete everything on the Live Duo after transfer and continue or should I/do I need to format or reset in any way? I am just wondering if there are any hidden files or leftover files after I delete. If I had 3.8TB and I deleted, will I simply have an additional new 3.8TB of space?

Thanks all.


Deleting the unwanted files should do.