Welcome to Clublexus. Just a couple of tips.
Search Google prior to posting any questions. If you have no luck. Check the owners manual. If that doesnt have it. Use the search function on Clublexus.
Every question you could possibly think of asking. Ever. Has already been answered. This way you wont have to wait.
1) Remove rear tool tray( NAV DVD player is underneath)
a)fold down rear seats
b)find velcro tabs on each side of rear tray cover where it meets back seats
c)lift velcro tabs
d)slide fingers gently along edge where rear cover meets rear seats to release 5 plastic push pins.
e)Use 12mm socket to remove the 2 now visible hinge bolts
f)remove tool tray cover
g) remove tool tray, There are 2 black push pin on both sides that pry up easily. NAV DVD player should now be visible on passenger side
2) Put ignition in ACC position
3) If there is a dust cover on unit remove it. Mine did not have this. Some do.
4) There should be a "slide type button" on your left of the unit. Slide this button to your left(facing unit). DVD should eject
5) Insert new DVD
6) Slide button back to original position
7) allow NAV to update before turning off ignition( check NAV Screen)
8) Reassemble in reverse order.