If you pay with a gift card and you use up the included hours, you can upgrade your current period to keep listening and reading instantly. If you have a Premium gift card and use up your hours, you can buy extra hours. To upgrade or buy hours you need to add a valid payment method to your account first however. You can do this under "Payment Method" on your account page.
Once you have registered a payment method, you can click on "Gift Card" in the menu, choose the new subscription type and pay the difference to the higher price calculated by how many days that are left in the current period. To buy extra hours for your Premium gift card, you head to the "Subscription" section.
If your gift card stretches over several months, you will have to upgrade each period separately. If you redeem a new gift card, it will only be activated once the current period has run out.
Gift cards are only available for the following markets and have to be bought on the respective website: Austria, Belgium, Denmark, Finland, France, Germany, Italy, Netherlands, Norway, Poland, Spain, Sweden, Switzerland, United Kingdom
Gift cards are not transferable between markets.