Whoa... wait a second. The existing DVD's are for pre-2004 Navigation systems only. As far as I've been told, there aren't any updates yet available for 2004 or later Nav-equipped vehicles. And yes, if and when one becomes available, it should only require inserting a new DVD. Keep in mind not all Lexus owners have the skills to locate the DVD player (in the trunk, etc), unscrew the mounting screws, tilt the player up, unlock and eject the existing DVD, insert the updated DVD, watch the LCD screen for instructions, replace the screws and trunk mats, etc.
I own a 2004 LS and haven't gotten any letter from Lexus about an available update! What model and year of Lexus do you have?