You can update the currency symbol for the chart pages by looking at the data file for that chart and that page.
For example, to change the currency symbol from $ to £ in the orders_Chart.php admin page you will need to open the data file for the second chart. This is in DynamicWebCharts > Data > orders_Chart_data2.php.
In here on line 118 you can update the dollar to the pound.
You could also do a site wide find and replace for this:
This should update all of the chart feferences.