what should I do to cancel my student visa and apply for Work permit visa?

I stay in China as a student. My course during time for three year. Here I stayed more than one year half months. Right now I'm trying to cancel my student visa and apply for work visa. So before complete my course if I want to apply for work visa.If I don't get any Chinese company helps so In China have any opportunities for foreign students to apply for self employed Visa? What should I have to do first and what documents needed for cancel my students visa. if I take this step what trouble I have to face in processing?