To access it, you will need to remove the center console trim. This can be done by prying it up with a plastic pry tool.
Once the trim is removed, you will see the navigation unit. It is held in place by four screws. Remove these screws and the navigation unit will come out.
You can then disconnect the navigation unit from the wiring harness and remove it from the vehicle.
To install a new navigation unit, simply reverse the removal steps.