De-authorise iPad

Hi,

I am contacting from Elsevier.

I have a customer who is using Adobe Digital Editions to read his previous purchases (E-books). However, he has already authorised 3 things (computer, iPad, etc)

He has since bought a new iPad which he wants to authorise with the same account in order to view the products. Therefore:

a) Does he de-authorise the other iPad to free up one "authorisation"? If so, how is this done?

b) If the item cannot be de-authorised (broken or lost) how can it be de-authorised?

I would appreciate a rapid response please.

Kind regards,

Josh Bayliss