You cannot delete or modify built-in roles. However, you can incorporate the built-in roles into your existing delegation model or use these roles to design and implement your model.
You can use built-in roles in the following ways:
Associate a built-in role with a user account or assistant administrator group. This association provides the user or assistant administrator group members with the appropriate powers for the task.
Clone a built-in role and use that clone as the basis for a custom role. You can add other roles or powers to this new role and remove powers originally included in the built-in role.
For more information about designing a dynamic delegation model, see Understanding the Dynamic Delegation Model.