When you have more than one series you can have a different chart type for each series. In this example I'll show you how to change one series to a histogram. You will also see how to add a separate 'Y' axis for each series.
Right Click on the series you want to change.
Then select the type of chart that you want to apply to this series.
Pass your mouse over the image to see the chart. I selected a 'column' type.
If you want a different scale for the second series, right click on the series 'Format Data Series'. Then change the radio button to 'Secondary Axis'.
Pass your mouse over the image to see the modified chart.