Downgrade from IredAdmin Pro to free

==== Required information ====
- iRedMail version (check /etc/iredmail-release): v1.4.2 (PostgreSQL)
- Linux/BSD distribution name and version:
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): PGSQL
- Web server (Apache or Nginx):Apache
- Manage mail accounts with iRedAdmin-Pro? Yes
- Related log if you're reporting an issue:
====

I dont use any of the pro features and would like to downgrade from pro to the free version.
is there a howto on how to do it?

Thanks