What is EC rebalancing? EC rebalancing is a StorageGRID procedure that might be required after a Storage Node expansion. The procedure is run as a command-line script from the primary Admin Node. When you run the EC rebalance procedure, StorageGRID redistributes erasure-coded fragments among the existing and the newly expanded Storage Nodes at a site
I'd definitely recommend upgrading to StorageGRID 188.8.131.52 and then running the EC Rebalance. You get some nice graphs in the Support > Metric > EC Overview section that give you progress status and estimated completion time details.
If you are using Erasure coding then you can make use of the EC rebalancing as mentioned above. If you are only storing replicas, then it is a bit more difficult to rebalance the stored objects. You can override the read-only watermarks under Configuration/Storage Options. you can also adjust the alert thresholds in Alert/Rules, but as long as there are sufficient nodes with free capacity to to meet the ILM rules, there is no need to do anything about the older full nodes.