What I pretend you help me is:
How can I change size of a set of icons from 32×32px to 16×16 inside a psd layer, with multiple layers(each layer is a icon).
Merge layers, resize
Just go through menu Image> Image Size and set 50% for both width and height. This will resize all the layers of document.
However for a 32 into 16 size conversion, probably you will need a complete redesign since you are doing it for icon. Direct resize of 32 into 16px can remove most of the detail and will not look crispy. In the Image size settings, try with “Bicubic Sharper” option for some improvement.
but some images don’t have the same size. Is possible select layer I pretend change size?
^ In such case, the only way is handling it layer by layer. First drag one icon layer from original psd into another psd without bg. Then Trim (Image > Trim) it to remove excess space and then set Image size into 16px. Do it for each image individually.