Sally,
Go to the web page for one of your Yahoo groups.
Click on "My Account" at the top.

The top entry has your name as it may appear on Yahoo lists. If it is not the name you want, scroll down to Address/Contact Information and click Edit on the right. The next page will allow you to change your name.

If this doesn't work, I actually don't quite know what to do. If it's specifically a class, you might want to contact Gretel (gretelob@gmail.com) to see if you were signed up manually.

Kitty