1. You receive Premium key look like: 688md7hp6cdfiqkdh
2. You should be log in at https://katfile.com/login.html
or create new account https://katfile.com/?op=registration
3. Access "My Account" to activate your Premium key: http://katfile.com/?op=my_account
4. Enter Premium key in field with description "Apply Premium Key" and click "Apply" button