What is the Workout plan for me? Please help?

I am 72 kg and my height is 5"5' .My waist is 36 and my age is 15.I have a manual treadmill and its quite hard to workout on it due to knee pain and i am also not adapted to it.I want to lose 20 kg till november .If i could lose fast then more good.But i need to reduce fast atleast 10 kgs till before 15th October.I can workout hard.I also need to reduce my waist.My treadmill has also got twister and stepper.I can work quite hard.Please suggest me a good diet too.I goto school everyday.Thanks for answering and dedicating time your time.