I've got the Birdview system in my 2004 Zed and have previously enquired about updating it from Nissan ..
Depending on which unit you have, there are only a limited amount of update options ...
For my older Xanavi unit (remote controlled) .. Nissan quoted me somewhere in the region of £300 for the update DVD ... and even then the maps were only the 2006 versions ...
The whole unit would need changing if I wanted current maps ... It's been mentioned many times before but I think it's by far the best option to go for one of Nurrish's systems ..
Might be worth calling Nissan to see what they say though ...