Ctrl-Shift-D on Windows, Cmd-Shift-D on the Mac.
NOTE: This only removes the activaiton information on your computer, and it does not give you an activation allowance back. Which is to say if you do "unregister and then reactivate with your AdobeID" 6 times, you will have used up all of your activations and will need to contact tech support (http://www.adobe.com/support/digitaleditions - click on 'Submit a web case') to get your activation counts reset.
mr. lester the problem that i had is now fixed.thank you for the help
I dont see a "submit a web case" on that page