I am not able to traverse from the last step to the first step in a multistep form
The example module uses a value stored in $form_state['storage'] to indicate which step the form is in, when it is being built. You could add a button with a custom submit handler that unsets this value or set it to the value needed for the step you want to show. Also remember to set $form_state['rebuild'] = TRUE;.

On a side note, if you want to make multi step forms, the ctools multi step form wizard API can help you doing a lot of these things for you.