Hello,
To achieve your goals, and become a successful IPS, you need to crack the civil service exams, this exam has 3 rounds, 2 written papers and 1 round of interview. You advance to the next level only when you pass the first one. You can opt any subject of your choice in the theory paper.
For a better preparation, join a reputed coaching institute which would help you crack the UPSC exam.
All the best :)