Hi I am a student in Canada..I am here since sep 2010...i got visa for 2 years.I want to change my study permit status to work permit....how can i do that.

Assuming that you have not graduated, you would need a job offer from a Canadian company as a starting point, followed likely by a LMO and then the work permit itself. Otherwise, after graduation, you could become eligible for an open work permit of up to three years.