If you'd like to leave a course, the teacher (course admin) must remove you from the course. Please contact the teacher in-person, or send the course admin a message through Schoology. To find the course admin of the course, click on the Members area on the left menu of the course profile. The member with the yellow crown to the right is the course admin.
If you'd like to leave a group, click into the group profile, and click on the Leave this group link located toward the bottom of the left menu.