Depends what you want to do with it.
If you want to change the options for a particular step (for example if one of the steps is resize the image to 800pixels, and you want to change it to 700 pixels....)....then Im afraid you cant just click a box and enter a new number.
If you want to change one particular step, just highlight it, click the flyout menu at the top, and select "Record Again", and it will allow you to record that same step again.