Of course, being self-taught in Photoshop, I had to muddle through learning to use the shapes. I'm sure there's a better way to do this, but I select my shape, then, in a new document, click and drag the shape until it's the size that I want. Then I ctrl+click on the shape layer to select it, and create a new layer. I fill the shape in on the new layer, then delete the shape layer. It's clumsy, but it works.