Extend visa

Hi there, i am a student and have a study trip for one week in one of the university in Wuxi. However, i am planning to extend my stay for 2 more weeks to explore other cities in China. I understand that the tourist visa is only for 15days, hence i would exceed the maximum stay for tourist. In this case, what is the best action to take regarding the visa? Do i extend my tourist visa before going or do i apply student visa?
Kindly advice, thank you.