The Exit & Enter Department is an office of the Public Security Bureau, it is under the management of PSB.

Generally, the extension is 30 days or less stay duration, you need to bring your passport, fill one visa application form, one passport photo, the accommodation sheet from an accredited hotel or from the local police station. It takes one week for the extension processing.

It is very very hard to upgrad your tourist visa to a student visa within Mainland China, you can find a qualified visa agency to do it for you.