Be VERY careful.
Your right to live and work in NZ entirely depends at the moment on working for THIS employer, the one named on your visa.
The following links tell you the official position.
http://www.dol.govt.nz/immigration/k...base/item/1187
http://www.immigration.govt.nz/migra...anotherjob.htm
http://www.immigration.govt.nz/migra...haschanged.htm
If you just LEAVE your present job, when it comes right down to it, you become a law breaker, because you are in NZ without a valid visa. You could find that INZ tell you to leave the country at any time, although in practice, they allow a bit of time for such a person to try to sort out their situation. (It doesn't say anywhere publicly exactly how long it will be.)
It would be much safer, and keep you within the law, to try to look around for another job while still doing this one.