Click the name of the desired layer in
the Layers panel. Then choose Object > Arrange >
Send To Current Layer.
Drag the selected-art indicator , located
at the right of the layer in the Layers panel, to the layer you
want.
You can move objects or layers into
a new layer by selecting them and choosing Collect In New Layer
from the Layers panel menu. Hold down Ctrl (Windows) or Command
(Mac OS) to select nonadjacent items; hold down Shift to
select adjacent items.