You have the option to change your URL at any time, but be warned! If you've already printed up business cards or other collateral, it may not be useful once you've changed your URL!
You can change the first part of your website address. There is no charge for this. In the app, go to Settings -> Website Info -> Change My URL and follow the instructions to update your site address! This is especially helpful if you've misspelled the name of your business, because you can quickly correct the typo and get moving!