Overriding the animation movement speed using transform

Hi all, I have a character that is being moved around the gameworld using its animation.

ie. I have a bool that sets the walking state and the character moves at the speed of the walking animation.

Now, what I want to do is be able to tweak the move speed with a float value, but when I use the following code, it still moves at the same speed as the animation.

 if (Input.GetButton("Forward"))
 {
 transform.position += transform.forward * Time.DeltaTime * runSpeed;
 }

So my question is, how can I tweak the animation speed of the characters walk anim?

Many thanks :)