The email address at which you'll receive submissions through your forms is the same email address stored in your site contact information (and, if you have chosen to display it, the email address displayed at the top or bottom of every page in your site).
You can change that email address in the Contact Information dialog (where you can also update your business address), your form settings, or the Add a Page dialog box, when you add a new form page.
To change your email address from any page:
YSS Element Label
YSS Contact Information Link
YSS Contact Information Dialog Box
Note: Your Yahoo! Site Solution contact information is independent of your Yahoo! account. To update your Yahoo! account, visit your Yahoo! Account Info page. Learn more.