To edit an existing chart you will want to find the respective chart on your dashboard or Update. From here you will want to click the dropdown "..." on the top right and select "Edit" as shown below:
After you click "Edit", the chart editor will appear on the right of your screen. You will automatically be directed to the "Metrics" section.
From the "Metrics" section you will be able to add or remove existing metrics, change metric colors, chart metrics on a different axis, or chart any of our automatically calculated Business Intelligence metrics.
You will also see "Options" and "Export" tabs across the top. The export tab allows you to simply export the chart. The "Options" tab (shown below) allows you to change the chart title, chart type, stack type, display period, edit the display period, add a chart annotation, and a goal line.