I'm in danger of failing my classes.
Why do you think you're going to fail?
Because I don't study as much as I should.
Sounds like you have the solution to your problem. Now all that is left to do is to try and change your views on studying! Schooling is important after all.
I'm lazy and don't have time.
Being lazy isn't really a good excuse though. We ought to make time for the things that are important to us. You should make your education a priority and study more.