Making Moderator and up ban users

Hey Guys Im having problem making my moderators have the ability to ban members.

I have these groups: Assistant,Contributor,Moderator,Super Moderator,Admin,Root Admin (Me)

now the problem is that the moderator and up can't ban members who are below Moderator. only me can ban users.

So how can i allow moderators and up to ban members in my forums. Im kinda new to making forums so please tell me how. and my site is phpbb3...


Thanks!

General>Forum>Security
Disallow moderators to ban members: No
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