You can easily change unit size or price at any point during a customer's subscription. Navigate to the subscription you wish to change and select Edit Unit Type.

You can then select a new unit size or price. It will give you the option to change to any of the unit types and prices you have created.

You will be asked if you want this change to start Immediately, On next renewal, or Backdate. You will be able to preview these changes before confirming.

If you select 'immediately' a pro-rata bill will be generated. If the new unit is a larger and more expensive then a bill will likely be immediately due. If the new unit is smaller and less expensive then the customer will likely have credit placed on the account.

Please ensure to change their unit allocation if necessary. This may require you to remove the customer from their current unit allocation and allocate to a new unit.