Currently there is no default pre-defined dashboard in Veeam Reporter, so it looks like you've already created some reports and placed them on the configurable dashboard.
Actually, there are two ways of creating widgets, some reports contain pre-configured ones, while others do not. You can find more info about Dashboard possible customizations in our User Guide
(starting from page 68)
As regards graphs representation, then, unfortunately, there is no way to show TOP N objects on the widgets, but as a workaround you can choose a reporting scope for the report and then based on that info create any custom widget.