We can choose which permissions are associated with these permission levels (except for the Limited Access and Full Control permission levels) or add new permission levels to combine different sets of permissions. We can associate permissions with permission levels and also associate permission levels with users and SharePoint groups. Users and SharePoint groups are associated with securable objects such as sites, lists, list items, libraries, folders within lists and libraries, and documents.
-: How to Delete a permission level:-
§ On the Site Settings page
§ In the Users and Permissions section
§ Click advanced permissions.
§ If the Settings menu is not available, select Manage Permissions of Parent from the Actions menu.
§ On the Permissions page
§ On the Settings menu
§ Click Permission Levels.
§ On the Permission Levels page
§ Select the check boxes for the permission levels you want to delete, and then click Delete Selected Permission Levels.
§ Click OK to confirm.
If you have any queries/questions regarding the above mentioned information then please let me know. I would be more than happy to help you as well as resolves your issues J J