How do I get the power aerial to go up and down? Does it operate automatically?

 

If you are talking about the power antenna, yes it automatic. As soon as the radio turns off the antenna goes down.

 

If the antenna motor does not work, you can always pull it up manually. You may need a "hook" to reach inside the antenna bezel however.
I got tired of seeing mine go up every time I played a CD, so I unplugged the motor. You may want to check to see if that was done on yours.