You can change your plan at any time under Your NetNav plan in the app's menu.
Upgrades (a bigger plan, monthly to yearly, or adding a website) start straight away. Paddle charges the difference for the rest of the current period, using the card on file.
Downgrades (a smaller plan, yearly to monthly, or removing a website) start at your next renewal date. You keep your current plan until then, and nothing is credited. If you would then have more websites than your plan covers, you choose which ones NetNav stops scanning; nothing is deleted.
You can cancel at any time under Your NetNav plan in the app's menu (Cancel plan, or Manage billing). Your plan keeps running until the end of the period you've paid for, then stops. Until then you can change your mind and keep it.
When a plan ends, NetNav shows only the plans page, as at the end of the trial. Your results and history are kept, and you can still download your data or delete your account.