To increase the amount of medication you receive each renewal would require selecting a new prescription and canceling your current one. You can do all of this in your account!
To cancel your current subscription, in your dashboard head to the Manage Subscriptions section and click the Manage Prescription and there you will see the Cancel Subscription button.
Once that is completed you would click on "+Add new prescriptions" on the homepage of your dashboard. You will need to fill out a new form and select your new amount in the How many uses per month do you anticipate? section of the form.
Once you've completed these steps be on the look out for email confirmations.