How to erase computer authorization

[LooieDawn]

My grandson set up his adobe digital editions account on my mac. Now when I try to download an ebook borrowed from the public library I get an 'Error getting License' message. I spoke to Adobe Support and they suggested doing an Erase Computer Authorization. My grandson has logged on with his  login ID and password but it won't let us erase his default profile. Does anyone have any suggestions

[Nanaky]

    quit Adobe Digital Editions.

    Navigate to /Users//Library/Application Support/Adobe/Digital Editions and drag the activation.dat file to the trash.

    If you are using 10.7, see https://helpx.adobe.com/x-productkb/global/access-hidden-user-library-files.html

    Open Adobe Digital Editions and reauthorize.