To select a plan, click on Settings Icon Account Settings in the account menu. 

This brings you to the Account Settings screen. Click Billing and Usage.

Click "Choose a plan" button

Select a plan from the three available tiers "Starter", "Pro", or "Premium"

Select a billing frequency.  Save up to 15% by selecting annual billing.

Enter your billing contact information

Add a credit card account for payment processing.

Click the "Confirm Plan Selection" button to complete your account plan setup.