You can mange or update your Bible Gateway Plus membership between monthly and yearly from https://www.biblegateway.com/user/account/. First, sign into your account in the upper right corner, click your name, and click Account Settings. Enter in your password and click Confirm. On the next page, scroll down to the Bible Gateway Plus Subscription section and click the "Change to Yearly/Monthly Subscription" button. When upgrading from monthly to yearly, you will be shown the following prompt.
Click Update Subscription. Your account type and charge amount--as well as the date of your next payment--will now reflect your new subscription type. You can always upgrade and downgrade your subscription, but your current subscription period will come to an end before the next charge is made to your card.