how can change min_passwd_length instead of 8 ?

Hello
I installed iRedMail-0.8.7 with ldap on ubuntu server 12.04.lts.

I want to change min_passwd_length ( you know it is 8 as default )

I changed /usr/share/apache2/iRedAdmin-0.3.3/settings.py by vi  but the iredadmin still wants min 8 chars.

how can i do what i want ?

Thanks