Select the Gradebook tool from the Tool Menu of your site.
Click the Choose File button to browse for and select your import file.
Note: The import file must be in a specific format in order to import correctly. It should be a CSV file and contain the appropriate student and gradebook item data. See How do I format my file for importing grades into Gradebook? for more information.
After locating and selecting your import file, click Continue to import the grades.
A summary of changes will be previewed for you. Check the box next to each of the items you would like to create or update. Then, click Next to continue with the import. (If you notice any errors, click Back to abort the import process.)