If your organization or business unit is set to only host free events, an attendee can opt to cancel their own registration.
To accomplish this, an attendee would need to sign into their account by selecting the "Sign in" link from the navigation of the event website.
Next they would need to select the "Welcome" menu item.
Selecting the "Welcome" menu item will take them to their Account page. From there, they need to select "Cancel my registration".
Finally they will need to confirm they wish to proceed. They will retain their member account within the organization, including their login credentials, but will not longer be registered for the given event. Note that this action cannot be undone.