You can control horizontal spacing. There is more information about this here.
You cannot as yet control vertical metrics (the spacing between lines or the effective "size" of of your letters) or kerning. We hope to add some form of control over these at some time in the future. Until then, you will need to download your font and edit it in desktop editing software in order to have full control over metrics.
Please contact us if you can’t find the information you’re looking for here.