Rebalancing is the process of periodically reviewing and updating the constituents of a smallcase. You can see the next expected update date on the smallcase page under the Stocks & Weights tab
This is done to ensure the stocks & weights in the smallcase continue to reflect the underlying theme and model
When a smallcase you hold has been rebalanced, you receive a Rebalance Update notification for the same via e-mail
You can now see the changes made by the update, make changes if you wish to and then apply them.