Hi. I have am on my spouse's work z visa. I have 3 mth contract to work now how do i change visa?

Since your are holding a spouse z visa, there is the possibility for you to apply for a China Work visa from the Exit and Entry Administration office under the Local Security Bureau in China with the Alien Employment License of PRC and Invitation Letter of Duly Authorized Unit provided by your employer, your passport and your spouse Z visa. But there is also the chance that your application will be refused, then you will have to go back to your country to apply for the work visa from the China Emabssy or Consulate general there. Anyway, good luck!