Reasons Why You Should Do It

Grades are very important as you need a C or higher to complete each course. Using your hacking ability, you can change your grades if you want. You can improve your grades or make them worse(I don't see why you would want to though).

Having good grades can help you graduate high school and that universities may accept you if your grades are outstanding. This is, however very risky because of the major consequences if you get caught, which you can read more about at the "Reasons Why You Shouldn't Do It" link at the bottom.

If you change someone else's grades such as your friend, depending on the individual, he/she may appreciate what you have done.