Tasks under Costs area to be removed in Custom Role

Summary

Some Tasks under Costs Work area in Projects Module need to remove from custom role

Content

we have created custom roles in PPM module & we have to remove some tasks under Costs Work area--Manage Accounting Periods , Manage Burden Schedules, Test Burden Cost Calculations but not able to do. when ever i am trying to delete the related Priviledges , it is showing that -It can be deleted from current role only.

 

Can anyone help me on this