If you have received a coupon or invite code, you can redeem it by visiting the following page. You will need to sign in to redeem a code, unless you are already signed in.
What happens next?
Depending on the type of code you redeemed, you will either:
...have a coupon applied for future payments. In this case, visit the Premium page to subscribe. If you are already subscribed, the coupon will be applied to your next payment. Please note that coupons to not apply to payments using PayPal.
...have access to a new feature. In this case, you should have received instructions along with the invite code how to access the new feature(s).