In the Project window, open the .psd Layers folder/group, right-click on a layer and select Reload footage.
To add new layers to AE: Create additional layers in the .psd, go to AE Project window, open the .psd Layers folder/group, ctrl+I to import the same .psd.
This time, select Import As “Footage”, in the next dialog, under Layer Options, select Choose Layer: ‘theNewLayerName’. I haven’t figured out how to import multiple new layers though…