You can edit most application details like the name of the student, or the responses to sibling questions etc from the student profile at any point in time. However, you can only change the status of an application that is in Submitted, Offered, or Accepted status.
To do this:
1. Go to the Student's Profile.
2. Click on the edit button next to listed School or Grade.
3. Pick the new School or Grade and click Done.