Click the tab of the layer you want to make active.
or
Click the Layers button
.
On the Layers dialog box, click the name of a layer, then click Set Selected Layer to Current.
Or double-click the layer name.
You can easily move from layer to layer with the keyboard shortcuts SHIFT+PAGE UP and SHIFT+PAGE DOWN. Press SHIFT+PAGE UP to move to a higher-numbered layer. Press SHIFT+PAGE DOWN to move to a lower-numbered layer.