Making self-balanced robot to move

Hi, I have made a self balancing robot based on one of the codes originally created by Jeff Rowberg. Self balancing works well, but how I can make the robot to move either forward or backward? What of the numerous parameters I should change?

For the robot to move forward you need to get it to tilt forward a little and then it has to run forward to stop from falling on its face. And that is also how humans walk and run.

...R

OK - thank you for your advice!