For subscriptions purchased via Website:
To upgrade from Plus to Premium, you can do so via our website. We'll automatically calculate the amount of time you have left on your existing subscription, as well as the amount you paid when you first subscribed when calculating the upgrade price.
For subscriptions purchased via App stores:
Unfortunately it is not possible to upgrade within your appstore. However, you can simply upgrade from Plus to Premium through our website and we’ll automatically adjust the amount you already paid for Plus in the new upgrade price!
Please keep in mind that the upgrade will start a new 12-month cycle in this case and that you must manually cancel your initial in-app subscription within your appstore after the upgrade. We're not able to cancel those on our end.