Making things more simple for you is the name of the game, so we've streamlined adding add-ons to members, and updating their membership plans.
See below for links to the new way to update your members plans, and add-ons.
Changing a Member Plan:
http://help.smpl.io/knowledge-base/change-membership-plans
Adding & Removing a member add-on:
http://help.smpl.io/knowledge-base/adding-to-and-updating-a-members-add-ons