To set the minimum password length you can put this in your qa-config.php file:
define('QA_MIN_PASSWORD_LEN', 8);
However, 8 is already the default in Q2A (since v1.8.0). I'd suggest keeping that and not changing it to 6 as that is less secure.
For changing password requirements you'll need to make a filter plugin with a validate_password function. Something along the lines of
public function validate_password($password, $olduser)
{
if (!preg_match('/[A-Z]/', $password)) {
return 'Password must contain at least 1 uppercase character';
}
}