I am not quite sure what you mean, but there are a couple of possibilities:
You want to make the whole chart bigger. To do this, run the dashboard or report, then draw your mouse over the lower portion of the chart. At some point, a gray horizontal bar will appear - grab and drag it downward to increase the height of your chart.
You want to change the scale of the Y axis. To do this, run the report, then choose Formatting Options then Y-axis. You can set the minimum and maximum values for the Y axis, which should increase the range.
You want a particular bar to be taller. I don't think this is what you mean, because to do that, the data point simply must have a larger value!
Or maybe you mean something else?
Sorry for being unclear. I meant I want to set the width of the bar in a bar chart. I'm using advanced XML and I've tried
<param name="charting.chart.columnStyle.width">30</param> but it didn't seem to have any effect. I'm creating a dashboard and displaying multiple charts/stats in a single row. For appearance, I do not need the labels on the Y axis because the needed values are already in an adjacent table so I have removed them in CSS. Now I want to adjust the width of the bars/rows in the bar chart so that it aligns properly with the other tables.