If you need to remove an attendee from your event, the way to do it depends on how the attendee was assigned to your event.
Attendee has registered through the registration site
If you want to remove an attendee who has registered themselves through the registration site, you do it here:
Free registration: Reg. Site -> Free registration -> Order history. Find the relevant order and click ‘archive’.
Billing registration: Reg. Site -> Billing module -> Billing list. Find the relevant order and click ‘archive’.
Attendee has been imported or added directly to the attendees list by the organizer
If you want to remove an attendee added directly to the attendee list, we recommend that you do it by un-assigning the attendee from the event, rather than ‘deleting’ the attendee from the attendees list.
You un-assign the attendee here:
Modules -> Attendees -> Assign attendees
Read more about Assign attendees here