The Days to delivery, Meals Per Day, Portion Size, Plan Categories and Categories/day values of a delivery date can only be changed while that day has no meals selected. If meals are already selected you either see the pop-up "To change the settings of the day of this subscription you must refund the selected meals first" or, when the change would reduce the day's capacity below the meals already chosen, the message "Need to refund N meals". Refund the meals on that day (Refund button per meal) and try again. The same protection applies to the per-day portion mix ("Meals are already selected for this day. Remove them before changing its portions.").