I have checked the official website, but it doesn't offer the possibility of deleting the account from the phone which means you will have to contact the developers of the application. To do this, you can use the Contact form through the link below.
Contact US: http://www.freepp.com/en/contact_us.php
Additionally, if the contact form is not suitable for you, send an email using the following address and request account deletion: android@browan.com