manage devices for activation

Many years ago I've started Adobe Digital Editions, activated it on some pcs, didn't use it on a regularely basis.

Now I'd like to revive my account, but don't know, how many pcs I've already activated - some might even be no longer available.

How to manage activated pcs with my current computer? How to find out, how many are activated, how to deactivated 'dead' devices?

Thanks