Capture the subjects and marks as per your progress report.  This means that an extra subject will be listed with only a grade 11 result for one and a grade 12 result for the other.  You will thus have 2 subjects with only one result while the remainder will have 2 results. Select the NV level for the Grade that you have not done the subject

e.g Changing from Mathematics (Grade 11) to Mathematical Literacy (Grade 12):

Mathematics:   Grade 11 mark: 7; Mid Year Grade 12: NV

Mathematical Literacy:   Grade 11: NV; Mid Year Grade 12: 5