You just change the cd in the nav unit in the boot. You have to remove 2 screws to enable it tilt up to access the front. There is a lock mechanism that you slide to one side to eject the existing cd. All you then do is insert the new cd and away you go. All the software updates are on the new cd and are auto loaded on insertion. I always find it useful to make a backup copy and use that, this keeps the original expensive cd safe. As to wheather it is a worthwhile exercise or not, the answer is yes, versions before 3xx where useless, anything ver3 onwards have much better software, and also include steet numbers. Dealer prices vary, may be as well to ring round, about £130 is average.