DNS cache TTL time on the DNS service.

[kinetica]

Hello,
I have Zentyal 3.4 as domain server and DNS server for my internal LAN
I would like to reduce the DNS cache TTL time on the Bind service.
As I work as web designer I often need to ask external domain administrators to change the DNS resolution
At that point from my local area I can not reach the remote site because my zentyal DNS cache is still caching the old IP
How can I reduce the TTL time?

my /etc/bind file looks like this:

include "/etc/bind/named.conf.options";
include "/etc/bind/keys";

// prime the server with knowledge of the root servers
zone "." {
        type hint;
        file "/etc/bind/db.root";
};

// be authoritative for the localhost forward and reverse zones, and for
// broadcast zones as per RFC 1912

zone "localhost" {
        type master;
        file "/etc/bind/db.local";
};

zone "127.in-addr.arpa" {
        type master;
        file "/etc/bind/db.127";
};

zone "0.in-addr.arpa" {
        type master;
        file "/etc/bind/db.0";
};

zone "255.in-addr.arpa" {
        type master;
        file "/etc/bind/db.255";
};

include "/etc/bind/named.conf.local";