Open Source Document Management System | OpenKM

After installing OpenKM, I found any users can create folders and files under okm:root directory.
I've tried to change UserRole permission to read only under okm:root, and even tried to remove it.
But it seems that I cannot change UserRole's permission under okm:root.

Is it possible to deny any users but administrator creating folder and file under okm:root directory?
Thanks.

Obviously by roles, the idea is remove UserRole and change to other roles ( users can have one or more roles ) and give them only read accessing revoking others.

If it's not possible to remove the UserRole, try to remove it from Administration => repository view => okm:root => remove UserRole from okm:authRolesWrite

No, you have to remove security of userrole and not from database!!!

I've tried adding another role AAA, let user A only belong to this role.
Set role AAA read only in okm:root directory.
The result still the same, user A can create file and folder.
Even worse, I cannot delete role AAA from okm:root's security setting.

I followed michaeled's suggestion, and successfully removed UserRole's privilege to create file and folder under okm:root.
Thanks.

I do not understanding why you can not delete with okmAdmin user the role AAA from okm:root's security ? which is the problem ?