You may need to edit your mark sheet because you entered wrong information about it, such as the wrong subject, term or even teacher. To Edit a mark sheet you click the List Mark Sheet link on the mark sheet tab of the east panel as shown below.
This will display the following window, that list all the mark sheets for specified teacher or all that you have created.
The List Mark Sheet window allows you to update and undo update your mark sheet as well as editing your mark sheet. Select the mark sheet record you wish to edit and click the edit link as shown above, the follow window appears allowing you to changes properties of the mark sheet.
Make the change and click apply.