I uninstalled the demo through Add/Remove Programs.
If you don't have any other sceneries using the Addon Manager (FSDT, Cloud9 or Skymakers), you should have removed the Addon Manager, when the Uninstaller asked you to do so. If you need it for other sceneries instead, read below.
However, everytime I start up FS9, after it generates the scenery file it tells me that KORD is installed but not activated. I press OK to not install then another message says that the scenery regsitry key has been placed in the FS9 main folder.
This happens because there's a serial number in the registry for O'Hare. When you are in Trial, there's no serial number in the registry for KORD so, if you Uninstall it, even if you DON'T remove the Addon Manager (because you might need it for other sceneries you have), the question to activate the scenery will not appear.
You might ended up in this situation, if you tried to put a serial in the registry, either by manually editing the registry, or by using the "Register Serial" option. Of course, if that serial is not valid or it has been activated too many times, it will fail the activation test, but you will still get the question.
To fix this, remove the serial number for O'Hare, by going into REGEDIT, and delete this key:
HKEY_LOCAL_USER\Software\FsDreamTeam\OHare
Removing the key will stop the program from asking to activate that serial.
