Hello,
You can rename your event at any time, by clicking on the event name in the event's management screen. If you're referring to the URL of that you selected for the event, this can not be changed once invitations have been send. Changing the URL after invites have gone out would break the existing invites, as the link they're expecting would no longer exist. Selecting a customized URL for an event can only be done before sending invites.
all the best,
the pingg team