Are you sure the map disc also in the drive? This should not be possible due to the 'gates' that come up and block the drive opening.
Assuming that there is only the Enya CD in there, the first thing to try is to get the Nav to eject it on it's own. Try turning off the ignition and leave the boot open. When the light on the Nav goes out after about 1 minute, press and hold the eject button. With the button still pressed, hit the unlock button on the remote, keep the button pressed for at least 1 minute.
If that does not work after a couple of attempts or you are sure the map CD is also in there, you'll have to manually eject the disc(s).
The exact mechanism depends on the type of Nav computer you have, I'll assume you have a MK III or MK IV. With the ignition off, open the boot and wait for the light on the Nav to go out. Feel round the sides of the Nav computer, you can feel some small barbed clips, 2 on each side. Press the clips in with your fingers and pull the Nav out. Disconnect the blue and purple plugs and the black GPS antenna coax. Prise off the lid, it just clips in place but you will break the tamper sticker. Looking from the front of the Nav you will see a small motor back right, it is held in place by one small Torx screw, a T6. Undo this with either a Torx driver or if you don't have one you may be able to do it with a small screwdriver that is exactly the right size. Lift the motor out slightly from the front exposing a white cog. Turn the cog clockwise until the disc comes out. Replace the motor and lid and reconnect the Nav.