SCv2020 Remove Enclosure

We have an SCv2020 with an SC120 expansion enclosure.  We want to remove the SC120 enclosureto be used elsewhere. 

I've cleared what should be enough of the data from the array.  Total space is 61.13 TB of which there is 15.74 TB of used space and 45.39 TB of free space.

What is the process to remove the enclosure?  All the drives are showing that they are 99% full.  I've tried to "release disk"  on one of the drives in the enclosure and it says "Releasing the selected disks will put the Storage Center below its low space threshold. Adding more disks may be required for a restripe to succeed."