To change your plan:
1) Log in to your account and click on My Account.
2) On the Left Side-bar, click on Plan & Billing and select Change Subscription.
5) There you will see a drop down with an option to switch plan.
If you are not seeing this option on your account, you are most likely not logged in as the administrator, but as a sub-user. Try to log into the dashboard using your administrative account information and you should see the subscription area.