Deleting
layers you no longer need reduces the size of your image file.
Select one or more layers or groups from the Layers
palette.
Do one of the following:
To delete with a confirmation message,
click the Delete icon. Alternatively, choose Layers >
Delete > Layer or Delete Layer or Delete Group from
the Layers palette menu.
To delete the layer or group without confirmation,
drag it to the Delete icon, Alt-click (Windows) or Option-click
(Mac OS) the Delete icon, or click the Delete key with
the Move tool active.