It depends on what year and whether it's electric or manually adjusted, but normally you remove the plastic cover on the inside of the car and unbolt it. If it's electric; disconnect the wires. If it's manual, pull the rubber handle off the adjuster and it should come away with the mirror housing.
Alternatively, you can ask the nice people at the scrap yard to remove it for you (I do this if I'm in a rush) but you cannot bargain on the price (which you should do with their first price!) I'd expect to pay no more than £25 for the pair with glass for manual and £40 for electric.
Mike, May 2011
