I have a bluetooth Apple Wireless Keyboard that is paired to a machine I cannot currently access to disconnect the keyboard. How can I unpair it from this computer to use it with another machine?
You need to turn it off (best to remove the batteries for a few seconds, then put them back), and then press and hold the power button on the keyboard.
If your paired computer is not in range, the keyboard's LED will start blinking and the keyboard will be ready for a pairing attempt with another machine. Release the power button and pair with your computer.