I'm supposed to be going to the 10th next year but I want to go back into the 8th because I feel like I don't no anything there teacher and no I don't want to go back to the 9th I want to start fresh is that posible?

No, you can't go back. Tell us what this is all about. What exactly is bothering you? Most teens want to hurry through school as fast as possible. Wouldn't it be weird to be older anyway, and with a different group?
If 9th was too hard, talk to your parents, guidance counselor, and a teacher you like about it. Tell us here what's going on.