Yahoo Mail account names can't be changed
Don't get stuck in the past just because your 12-year-old self thought your classroom nickname would make the perfect email address. While you can't change your Yahoo ID or email address, you may be able to create disposable email addresses with your existing account, or you can sign up for a new Yahoo Mail account.
The disposable email addresses feature is available to Yahoo Mail Plus subscribers and users with existing basenames and disposable email addresses. Users in Yahoo Mail Plus locales can try up to three disposable addresses for free. Yahoo Mail Plus isn't available in all locales. If the option isn't listed in your account, it's not available at this time.