For activity based rosters, it is only possible to delete a roster if you have not already created any shifts.
navigate to the roster group for the activity based roster
choose the 'Actions' button at the top right
choose Admin rosters:
Select the roster by clicking on 'view', then 'edit' and you will see a 'Delete' button in red at the top right:
If the roster has either published or drafted shifts, the delete button will not appear. Only if you delete these shifts, then you can delete the roster.
If you do not wish to delete the published or drafted shifts and will not be using the roster anymore, you can put an end date to the roster:
