In order to register Koru and remove logotype from exported files you need to purchase a license. Then, use Help -> Registration menu to complete the registration process. You will need a license key for that. Normally, you should find one in your purchase confirmation e-mail, if you don't - please contact our support team.
Copy your license key from the order confirmation e-mail to the clipboard and paste it to the Registration window. Click OK and restart the application.