You can switch plans any time from your subscription settings. There are two buttons that matter:
Change Plan — switch between plans (for example Pro to Unlimited, or monthly to yearly). Stripe handles the prorated invoice automatically. Manage Billing — opens the Stripe billing portal, where you can update your card, cancel, switch plans, and download past invoices.
Upgrades vs downgrades
Upgrades take effect immediately and you're billed the prorated difference right away.
Downgrades also switch your plan, but instead of a same-moment refund, Stripe applies a prorated credit toward your next invoice. So 'changes take effect immediately' is fully true for upgrades; for downgrades, the money side settles on your next bill.
Open subscription settings