I got an email from Proton to renew my account that included:

"Just log in at mail.proton.me, then go to Settings → Dashboard → Payment methods → Add payment method."

There is no "Payment Methods" entry in the menu.You have to guess which plan you currently have (I didn't remember), then go in and add a new credit card since it won't let you update the expiration date on the existing entry.
1. State clearly what the current account plan is
2. Allow updating of credit card info without reentering everything
3. Show when the account expires or how much time is remaining