How do you delete or remove a thread?

Not by yourself. If you click the little yellow triangle in the lower left corner of the thread or post and report the thread with the reason you wish the thread to be removed, the admin team will review your request and advise you of the decision. Threads are NOT automatically removed by request, it depends on the reason

Alternatively post in the Admin Help Desk if you do not wish to report it where we (the 7 Admin staff) can discuss reasons for removal