Hello Hirama666
There is a "- Delete" link next to the selected group.
If the link is missing, this is because there are some foreign keys constraints in the database referencing the marking periods in the group (or put differently, the marking periods in the group are in use).
Here are some examples of tables having Marking Periods as a foreign key constraints (not exhaustive):
- Course Periods
- Daily Attendance
- Course Period Attendance
- Gradebook Assignments
- Grades Completed
- Schedule
- etc...
You may try to delete it next school year after Rollover and deleting course periods associated to those Marking Periods.