When you want to re-use a past event, you just use the Save Copy button.

Do not just rename old events, as they will still have connected to them the tickets/registration sales etc that occurred. (You can of course just rename a past event if it has no ticket sales or registrations, as it's really just a listing).

Step by step

1. Edit the past event and start by clicking Unpublish so it no longer shows up.
2. Click the Save Copy button to make a fresh copy of the old event without the connected tickets or registrations transactions/data that have already happened
3. Close and open the new Event you will see in the list with the word "(Copy)" at the end.
4. Change the dates of the event and the on sale / off sale dates of the tickets.
5. Edit anything else you need to change
6. Save & Publish

Your old event data (like sales information, reports etc) are retained separately from the new event this way.