I would think you would 1)wire the big terminal of the starter directly to the battery 2) hook the small wire that controled the original solenoid to the small terminal on the starter 3) disconnect and remove the original solenoid.

As a test, before you do any of the above, put a test light on the small wire to the original solenoid. When the key is moved to start (or start button pressed) the light should light up. When the key or start button is released the light should go out. After you verify you have the correct start wire, have at it.

PS... a pic of your current setup, especially the old solenoid, would help.