Digital Editions 4.0 Licence

Hi,

I  am upgrading our PCs from XP to Windows 7. These computers already have Digital Editions 4.0 on them which we use to access CCH Master Tax Guide which we have 5 licences for. When I upgraded the first computer/user and re installed Digital Editions it told me I could not access the Tax Guide as I had used all my licences.

Is there a way of deleting/deactivating the licence before I do the upgrade so the users can still access the book on their computers?

Thanks

Michelle