3
Go to System Admin\Templates and find your cloned template set. You will notice an entry for 'Forum' which is of course the NewBB templates with about 11 or 16 entries in it (can't remeber which). Click on it, and then for each of the entries delete each one using the delete button. When you do that, the entry will change colour to yellow and the button will change to 'Re-Generate'. Click the button and it will be re-generated from the system template set.
I recommend you do them all at the same time though to make it easier to tell which one's you've done, although the new one's will get the current date, so ignore me!
Good luck.
Ted