How do I upgrade or downgrade my subscription plan?

Go to Settings > Account and scroll to "Subscription plans." You'll see all available plans (Free, Plus, Pro). Click the button on the plan you want to switch to. If you're upgrading, you'll be taken to a checkout page. If you're downgrading, the change will be scheduled to take effect at the end of your current billing period, so you keep full access to your current plan's features until then.