If you are on the Emerging, Achiever, or Innovator level, you can upgrade your account at anytime.
Log into your account and hover over your profile image in the top right. From the dropdown menu select My Account:
Scroll down to the Membership Plan section and click on Upgrade Membership.
On the following page you will be able to select the plan you would like to upgrade to.
Select one of the payment plan options (monthly, annual, bi-annual):
Important: All membership plans are a full one-year commitment, even if you choose to pay per month. You won't be able to cancel mid-term.