At any time, you can upgrade from your current plan to a higher plan.

Note that it's not possible to downgrade a plan. If you need to downgrade, you will need to cancel your subscription, then subscribe to the lesser plan when your term expires.

To upgrade, select the "Change/Cancel" icon for the subscription you which to change (you cannot make changes to a cancelled subscription).

From the Subscriptions page, you can click on the "Activations" button...

Then, select the upgraded plan from the dropdown:

The cost for your upgrade will be prorated depending on how many days are remaining in your cycle. Your credit card will be charged immediately.