Go to Sign-up.
Select the Sign-up tool from the Tool Menu of your site.
Click on a meeting title.
Click Copy.
Click on the meeting name to open the details, and then click the Copy link at the top.
Make your changes, then click Publish New Meeting.
You now have a display entitled Copy this meeting. Change the settings as desired, including the title if you want a new meeting name, and then click Publish New Meeting.
Note: Some settings will not be available to edit. You cannot copy a multiple-slots meeting into a new single-slot meeting, for instance.