Upgrading, invoices and cancelling
Manage the Teacher plan in Settings → Plan.
Upgrade to the Teacher plan in Settings → Plan; payment is handled by Stripe. In the same place, "Manage billing" lets you update your card, download invoices or cancel.
Cancel any time. A yearly plan runs to the end of the year you paid for, then you return to Free; nothing is deleted, and results older than 30 days are hidden until you upgrade again.
For refunds, invoices to a school, or anything about a charge, use "Ask our support team" and we'll sort it out personally.