Set your default academic system, add terms per grade, and indicate the Grade default per level. You also have the option of customizing what you call a particular grade. eg. If at your school, grade 12 is termed as year 13.
Go to your Account Configurations and scroll down to the section on Grade Default.
After making changes, don't forget to click 'Save'.
Note: Only Administrators have access to this page. Any changes made in Account Configure apply to all users associated with your account.