Select the Sign-up tool from the Tool Menu of your site.
Click on the meeting name to open the details, and then click the Copy link at the top.
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.