I want to change my spouse/dependent visa to Z type.

Nidhi, it depends on local entry and exit management bureau. If they agree to let you apply for the Z type without leaving, then you can change your dependent type into Z. If not, you need to bring all required documents to apply from Chinese embassy in your own country.

You need to find an employer and ask him/her to help you acquire te work permit. Then you can take the work permit, passport, passport photo, application form, temporary accommodation registration form to visit local entry and exit management bureau and then let them decide whether you can apply without leaving.