To see all of the activities and activity packs assigned to your students, click on "My Activities" on the teacher dashboard, then click "My Activity Packs."
From this page, you have two options: you can delete activities from an activity pack, or you can un-assign the entire activity pack for the students of your choosing.
To delete an activity from its activity pack, simply click on the 'x' on the right of the activities due date slot. This will automatically remove it from all of your student's assignments.
To un-assign an activity pack for specific students or classes, click on "Edit Classes and Students" in the top right corner of the activity pack.
From this page, click "Select by Student."
That will open up this menu. Uncheck the box next to the student's name for whom you'd like to un-assign the activity pack.