Go to your Rate Now tab (the red star icon).
You will see your rating To Do list; scroll down to your Done list. Here you will see all the ratings you've completed and are able to edit.
Click on the Edit button next to the rating you'd like to make changes to - you can adjust your 1 - 5 rating, as well as edit your comments.
Click Submit when you're done. You will be able to go back and edit all your ratings until the end of the current cycle.