1. You will receive a voucher / coupon like this ( login:password ) : tx39l3lunw9ddddd
2. Login into your account ( If you haven't account at https://filejoker.net/registration , you just need to sign up )
3. Make sure you are logged in, then open page: https://filejoker.net/profile
4. Put your Premium key / Premium code in "Activate coupon code:" and click on "Activate"
5. The account becomes Premium.