You can find the expiration date of your license key in Permalink Manager settings (“Tools -> Permalink Manager -> Settings -> Licence key”):
It does not matter when you renew the license, it will be always prolonged for one more year from expiration date. For instance, if you renew it on November 10, 2018 and it is valid until December 15, 2018, the new expiration date will be December 15, 2019.
To renew the license key, please go to Gumroad checkout:
Please copy the full license key from the “Licence key” input field in Permalink Manager settings:
After you select “License type” and click on “Buy this” button, an additional field “Your license key” will be displayed where you should paste the copied key:
Your license key will be automatically prolonged after the payment.