how do I get size of preexisting circularly shaped layer in photoshop

I am new to photoshop and not finding it very intuitive. How do I get the radius of a preexisting circle in photoshop? Someone sent me an editable psd, and I have the circle as a layer. Also is there a way to resize a circular layer to give it a larger radius or would I just need to recreate the circle?

Thanks very much for any help or tutorials you can point me towards.