If you are on the Pro plan, and need to downgrade to a cheaper plan, here is how to do it:
Go to your billing settings in your profile
Click "Manage payment settings"
Enter your email
Check your email for a Customer Portal login link
Click the button in the email that say "Log in to your customer portal"
Click "Update subscription"
Choose a plan you want to downgrade to
The portal will show you how your billing changes