How to extend Chinese visa

Hey I got an M type and my stay of duration is for 30 days I am still here in my country. And I wan go there and apply for language and learn but people there are telling me that I can't extend my visa after 30 days of stay so my question is for how long is the application going and how long will it take me to get an admission letter and the JW so that I can get a X type and learn there