2001 nissan pathfinder oem navigation

I found this forum looking for information on my navigation system.  It is the factory original piece.  The buttons have fallen off, which this unit is prone to do.  I hadn't bothered replacing the unit since I don't really use it and the car is almost 10 years old.  Now, however my AC has stopped working and the AC control unit and the navigation are one system.  I can't get the error code without a functioning unit.

I found a unit in a junk yard halfway across the unit, which is on its way.  I need help with removing the old unit and installing the new one.  If there is any information, or guides you can point me towards it would be appreciated.  I don't have any experience doing this type of work, but I do know a little about mechanics.

Thanks for any help you may be able to offer.

One more question please.  I can't figure out how to unclip the clock/vent assembly.  This is step A.  It looks like the rest should be pretty easy.

Thanks again for any help.