I'm holding S2 for 3 months

Yes, it is possible to change the S2 type to a business M type or a student X type. The first step is to prepare the required documents including your passport, the application form, a recently-taken bareheaded color photo, and valid registration form of temporary residence. For M type, an invitation letter from a business partner and its business registration certificate will be needed. For student X type, the admission letter and the JW form from the school will be needed.
Next step is to go to the local exit and entry administration to change the S2 type to M type or X type.

And can I go to hongkong and apply for a new visa to China?

It is possible, but it may not be that easy if you don’t have HK residence permit.

And what's the JW form?

The JW201 / JW202 is a form generated by a Chinese university upon admission acceptance. It is needed when you apply for the student X type.