If you need to change your subscription to add or subtract features such as Videos or Online Grading or even switch from Single Student to Family Plan or vice versa, first log in to your parent account. Then find the Account page in the main menu. Click Manage Subscription on the Account page:
On the next screen you can update your plan to whatever level you need.
Note: If you are trying to downgrade from the Family Plan to Single Student, first make sure you only have one active student on your account. To deactivate a student, click Edit next to their name on your parent dashboard. Once you have only one active student, you should be able to downgrade to the Single Student plan.