You will need the following items:
You will have to change the control on the tub to an air button. You will now only have on/off options instead of the multiple speed you currently have.
The link below shows a replacement pump and just under that shows an Air Button you can use and get some air tubing as well.
1 hp - http://www.uspartscenter.com/Gentekk_WP600W.aspx
1.5 hp - http://www.uspartscenter.com/Gentekk_1500W.aspx