To view a subscription, click the "View" button circled above in red. You will be taken to a page with information about your subscription and actions you can take with your subscription. In the middle of the page under a section labeled "Subscription Totals" you will see the following:
Clicking the "Change Your Subscription" button will take you to a page similar to the shop page for our subscription:
From here, you will choose the amount (note that all renewal frequencies are now a month by default) and then click "Add to Cart" as if you were purchasing a subscription. Once you complete the check out process with a new subscription selected, your old subscription will be replaced by the options you selected on the new subscription. This does NOT add a separate, new subscription to your current subscriptions. This will only replace the subscription you currently have.
Alternatively, you can request a change to your subscription through customer support by emailing or using the chat window on the bottom right of your screen.