To upgrade the current plan, open profile by clicking the top-right button next to your domain.
The next step is to click the Upgrade plan button.
You will see the plan manager and all plan options you have. Choose the one which is the best for you and click Choose plan button.
Enter all the required data to process the payment.
Once the payment is proceeded, your plan will automatically be upgraded.
Further on, you will be changed on the same day every following month.
Keep in mind, that by choosing an annual subscription, your saving is 16% comparing to a monthly plan.