First, click the My Students tab on the left navigation menu.

Then, click the My Co-Teachers toggle.

From the Teachers I Share With tab, click the trashcan in the remove column.

This will delete all of your students, groups, assignments, and data from the co-teacher's account.

From the Teachers that Share With Me tab, click the trashcan in the remove column.

This will delete all of their students, groups, assignments, and data from your account.