I am not sure what you are asking. Are you a teacher asking how to change a grade on one of the graded content types, or how to change a student's overall grade or what? Or, are you a student asking how you can change your grade on an assignment or quiz?
If you are a teacher, please clarify where you want to change a grade.
If you are a student, study harder and talk about this with your teacher. This is a global community of Canvas users much like yourself, and for these kinds of course-specific questions we are unable to help