Increasing / Decreasing Radius of Rotating Object

What I have currently is an object that rotates around a set point. What I would like to do is to be able to change the distance from the object rotating to its center. While the object is still rotating. At the moment I am just using a transform.RotateAround to get the orbit.

try to use the

transform.Translate(transform.forward * Time.deltaTime * speed,Space.World);

in this one you can put tranfroem.f.... a (-) to make it backward or you can use

tranform.localPosition.z += 0.5;

and you change the += to = to give it an specific Position.