Grades can only be removed from board level, to do this you will need to have the proper board level permissions. 

1. Log into the board > main menu

2. Click "Setup"

3. Click Grades >"GO"

4. Click "edit" on Grades offered at each school tab

Once this screen is in edit mode you can uncheck the grades you don't need or add the grades you need. This will automatically save your choices. Click close when done. 

Troubleshooting tips/issues: Your changes will not save and you get an error message

Review solution article https://sis.support.edsembli.com/en/support/solutions/articles/8000113272-troubleshooting-removing-grades-from-the-grade-table