You can purge cost types and all costs within the cost type. Or, you can purge only part of the cost information, such as make or buy items, resource and outside processing costs, overhead rates and amounts, or resource and overhead associations.
You cannot purge frozen costs in standard costing or average costs in average costing.

Based on rollup items, costs and controls: Cost information for based on rollup items, costs and controls associated with the cost type.
Cost type and all costs: The cost type and all associated cost information. This is the default.
Department overhead costs and rates: Department overhead costs and rates associated with the cost type.
Not based on rollup items, costs and controls: Cost information for items not based on the cost rollup, costs and controls.
Resource costs: Resource costs associated with the cost type.
Resource/Overhead associations: Resource/overhead association costs.