If your account is in Free Trial mode and you'd like to upgrade to Topspin, Topspin Plus, or Topspin Enterprise, just click "Choose Artist/Upgrade" in the top navigation bar: 

Choose the artist account you'd like to upgrade from the drop down menu and click 'Upgrade':

You'll be presented with a payment modal with upgrade options for Topspin, Topspin Plus, or Topspin Enterprise in a monthly or yearly billing schedule:

Choose your preferred Topspin plan, get your preferred payment credit card ready, and proceed through checkout. That's all there is to it! Welcome to Topspin!