First, click "Edit Dashboard".

Then, hover over the widget you want to customize, and click the ellipsis “...” in the top right-hand corner of the widget. In the drop-down menu that appears, select “Edit”.

An editing menu on the right-hand side will appear. The exact customization options available will vary by widget and metric.

Finally, apply your customizations by clicking “Done Editing” in the widgets ellipsis “...” drop-down menu, and click "Save" at the top right.