I'd like to know the same thing.

I've deployed a FS and know want to scale back / down the capacity. Is it possible or should I delete and redeploy?

@Nutanix: Possible Feature request?

You can reduce the quantity of FSVMs underpinning a fileserver (‘scale in’) or reduce the vCPUs / memory allocated to FSVMs (scale down), but you cannot reduce the storage capacity assigned to a fileserver. Having said that, all capacity is thin provisioned anyway. This means you only actually consume whatever TiBs of data are written by clients (plus snapshots), regardless of how much capacity has been assigned to the fileserver. Any unused capacity in the cluster can be utilised by other services running on the cluster (assuming it’s a mixed environment)  You can always set a maximum size for each share and to help even further with capacity management we also support hard and soft quotas. 

Hope this helps.