Select your contact under “My Book” and open their contact information panel.

In the “Summary” section (first tab), find the “Action Plans” section

Click on the pencil icon beside the action plan you would like to remove them from. 

Your Action plan manager will  open.  

If your contact is on any of these action plans, you will have an option to “Go” (under the View column), or to “Remove” (in the Assign column). 

Click “remove” to remove them.