You may have noticed that when you attempt to delete a layer that is being used by entities in your drawing you will be denied.
There is, however, an easy way to delete layers that are being used by entities.
The command is LAYDEL. Type the command and you will be prompted with this:
Select object on layer to delete or [Name]:
You can select objects on the layer that you want to delete or you can type N to select a layer from a dialog box.
Be ware that if you delete the layer, the entities on that layer will also be deleted.