Do you think I'll get caught if I use Photoshop to change my grades at the end of each semester?
I think you might get caught. Why do you want to change your grades with Photoshop?
My grades are bad and I don't want my parents to see what they really are.
Trying to hide your grades from you parents isn't appropriate. They need to know how you're doing and if you're struggling they can get you some help. Don't try to hide the truth from them.
I don't want to tell my parents what my grades really are, they'll be embarrassed.
I'm sure your parents will be upset, but they'll also be concerned about your struggles in school and want to help. Let them help you and you'll feel better about the situation.