How to clone an existing report
First, click the "Create Report" button from your Reports dashboard (or from within a campaign).
You'll enter the report creation wizard, and will be prompted to select a campaign, and to create a title for your report.
In the third step of the wizard, you can choose the "Clone existing report" option when choosing the source of your report.
Cloning an existing report will make an exact duplicate of that report, and you'll then be free to make any changes you like and save them as a new report.