Self-study first, ask school teachers to help 2nd, ask parents and older siblings to help 3rd, failing all that ask for one-to-one tutoring.
For math, buy textbook from Singapore to self-study. It will help as they have a complete system that provides textbook at the easy to read English kind.
For Maths, you could just probably self-teach/self-study. Although with sciences you may have to go a tutoring depending on how you're going at school. I recommend: PEAK Science, Matrix or Talent 100. If you are struggling then try a 1 on 1 private tutor.