First things first: sign in to your Yahoo! Mail account. Then:

1. Click Options in the upper-right of your Mail page and select Mail Options.
2. From the list on the left, click Accounts.
3. Click Add or edit an account.
4. Click once on the account you want to edit. Then click Edit. (To delete an entry, click Delete.)
5. Edit your settings. You'll recognize all the same options you had when setting up the account.
6. When you're done, click Save Changes.

Note: For security reasons, your password does not appear. If you need to type a new password, just type it in the space provided.