How do I up update email address for ADE when forgotten old log in

Am trying to set up ability to download ebooks for my kobo and have downloaded a couple of books in past but so long ago could not remember.  Went on kobo help and said I needed an Adobe ID and to download ADE.  I thought I might try to guess my old password re the ID but unsuccessful so decided to create a new adobe ID with my current email address. as could not ask them to resend as email address changed. I did not realise but had an old Adobe Digital Editions (and have successfully downloaded 2 books  long ago) which have updated with newest version but when I followed advice by Kobo to try to authorise my mac it was greyed out as ADE shows computer is already authorised under old email address and presumably old Adobe ID before.  What can I do so new email address entered on ADE ?  Help please