I have previously managed to edit the Page Views Over Time settings to show longer time periods, eg 30 days vs default of 2, or similar. But now I forget!

Recently noticed my 'by Month' tab has been losing data from the earliest histogram column. It seems it is only displaying data from the previous n months, somehow counting by days, so that the earliest column actually decreases over time.
Can someone please advise me where I can change these settings so I can view 12 months of data?
I have tried Manage>Dashboard>Customize, but this only allows minor layout and content changes.
As always, I appreciate your help
Stephen Barrett
New Zealand