Run the Report that you wish to copy.
Click the Save as link at the top of the Report view page. 
You have now created a copy of the original Report which you are able to rename: 
Click on Finish.
Once you have edited the Report (See the Edit a Report guide if you need further information), click on Run Report near the bottom of the screen.
Additional options
Share the Report
Tick the Share box under Who can run this report (see above image) to allow other Administrators to run the report.
Edit the Report
This allows you to amend the parameters, fields and filters. See the Edit a Report guide.