How do I configure Default Route from one router to another?

I am using Packet Tracer 5.3, and I was assigned to set up a network and I need to use Default Route.
I'm using a ROAS (Router On A Stick) router to an ISP router via Serial.
How do I do this step by step commands using Default Route?

p.s I attached the Packet Tracer file if it helps show what I am trying to do.
THANKS!

ip route 0.0.0.0 0.0.0.0 x.x.x.x
where the x.x.x.x are the gateway IP connecting to your service provider

Agree with charloe,

You could also post your pkt file here: www.2shared.com/ so we can help better.