How do I downgrade my account to a lower plan?

Click Account from the dropdown menu under your name at the top of the page.

Then click Subscription and Usage> Downgrade Plan.

This will bring up the pricing table. Decide which plan you wish to downgrade to and then select "downgrade" in the column of the plan you wish to downgrade to.

Up to the end of the current billing period, access to the quotas and features of your current plan will remain in place. At the renewal date you will be switched to your selected reduced plan, and your renewal payments will be at the new rate. You will be subject to the quotas and features of the reduced plan.