1. You will receive a premium key like this: 359zn3cjo8ud7wl8i
2. You should be log into your account.
( If you haven't account, you just need to sign up free account: http://worldfile.net/?op=registration )
3. Make sure you are logged in. Then access this link: http://worldfile.net/?op=my_account
4. Paste your Premium key in "Apply Premium Key" and click "Apply" to proceed.