Hi, jweaver0312 - When you select a plan, it should automatically redirect you to Manage My Plan page where you can add/remove add-ons. What happens when you choose a different plan/service if you already have something in your cart?
I was doing it while I wasn't signed in. So it brings me to the order service page, if i choose a different item, the item already in the cart gets replaced by the item i just picked.
@jweaver0312 - If you would like to compare different plans - click on Select to Compare. It won't let you have different plans in the cart because you technically cannot have Double Play and Triple Play on one account. If you would like to completely clear your cart - try to clear Cache and Cookies in your browser settings.