To make the width for the body of the candle chart wider, specify a larger value for the SymbolStyle.Size property like in the following code. Note, that the default value for the body width of the candle is 5.
c1Chart1.ChartGroups(0).ChartData.SeriesList(0).SymbolStyle.Size = 10
•C#
c1Chart1.ChartGroups[0].ChartData.SeriesList[0].SymbolStyle.Size = 10;