Undo 2 captive screws in the hard disk bay cover, and remove the cover.

Remove 2 screws securing the hard disk in its bay. These are the 2 black screws at the opposite end to the connector.

Disengage the hard disk from its connector by pulling on the black plastic tab.

If you are replacing the hard disk you will need to take the old one out of the carrier by removing the silver screws, and insert the new one in the same carrier. Make sure you fit it the same way round as the old one was.