Yes, you can. From your online account, choose the My Giving tab, where you'll find your Scheduled Giving. Click on the Update button next to the scheduled giving line you wish to adjust. If you sponsor multiple children, you must follow this procedure for each one.

To move all your currently scheduled donations from one payment method to another, stay on the My Giving tab and scroll down to Payment Information. First, be sure your new account has been added to your online account or click Add Funding Source to do so. Then, next to the account you wish to replace, click Replace. You can then choose a new funding source and move all currently scheduled donations.