Please login to your Mobicip account and go to My Mobicip > My Plans. You will have the option to upgrade to a standard or a premium plan from this page. It is advisable to use the original payment method to make changes to your plan. If the subscription is bought through the App Store or Play store, you can upgrade through the Subscriptions section in the Phone Settings app. 

If it is purchased on mobicip.com, please login to your account and upgrade options will be provided in your My Mobicip menu.