To assign or change Letter grades and GPA, select "Grade scale" from the "Grade" menu. To change the letter grading just click on "Reset" and enter new ranges by defining "From" & "To" percentages with their letter grades and CPA numbers. To delete the range shown (displayed on the top of the window) just click "Delete". To set changes or additions and go back to the main window just press "OK" at the bottom of the window.