Updating a value in a TAChart

[Leledumbo]

Let say I have a list box containing integers. The chart will draw the x-axis as listbox items value and y-axis as the number of appearance of that value in the listbox. I want to make such that when the items in the listbox is updated, so is the chart. But from the given methods, I have no idea how. For example, if I call TBarSeries.Add(aValue, aLabel, aColor) twice with the same aLabel but different aValue, instead of updating the old aValue, the chart draws another bar with the same aLabel but different aValue. So how do I do this?