How can i do better in my private school highschool?

I just got my grade back for the third quarter and they arent good. I am a freshmen in a private school in new york. But grades are suffering and i do not know what to do. My lowest grades were in chinese and math. i am scared ttthat if i get lower grades again they will think abut kicking me out of the school because that is what they do. I am really scared what can i do to raise my grades