There are many ways to revise for exams but we are going to give you a few tips:
Reading or Highlighting your notes is just not enough you need to write and re-write notes preferably trying to describe things in your own words. You could swap with a friend to see what they have done.
Start a long way out from the exam, "a little bit often" is the best way. It is easier to study 10 minutes a day for 3 months than trying to cram 2 hours in every day for two weeks.
Use the the "learning outcomes" or "arrangements documents" as a check of your knowledge, tick off the things you do know revise the things you have not ticked off.
Past Papers will help but only when you have done a fair amount of revision. They will show you what you need to revise. You need to get them marked in order for them to be any good. Your teacher will give you feedback and help you to improve your exam technique.
There is no substitute for hard work. Years of data tells us that if you work hard you will get better marks than if you don't.