Update: You can now configure the reports charts that are shown. [See more information in the Help Document][1] (scroll about half way down the page)
Right now you have to use a registry hack. See the bottom of:
[http://www.poweradmin.com/help/SM_4_1/Report_Server_Status.aspx][2]
[1]: https://www.poweradmin.com/help/latestsmhelp.aspx?page=report_server_status.aspx
[2]: http://www.poweradmin.com/help/SM_4_1/Report_Server_Status.aspx