This sounds less like an API question and more of a general use question (but by all means, correct me if I'm way off base). The token's appearance is dependant on the art you're using for it. So if you want a round token rather than a square, you need to upload/locate/purchase round images. There's several applications out there available online that can crop an image and make a bordered rounded token for you. There's also free image editing software out there like GIMP where you can create rounded token images.
