1. Logging on and signing in- Open your web browser and go to www.yahoo.com, click Mail, and sign in using your email address and password.
2. Inbox- Near the top right of your inbox, you will see your name and a gear icon to the right of it. Mouse over the gear icon and click Settings from the drop down menu that appears.
3. Settings- In the Settings box that pops up, click Writing email, which is the 2nd option listed.
4. Writing options- At the bottom of the Writing email options, you will see Signature. Click the arrow and select the plain or rich text option. In the text box provided, delete the former signature text and enter the new signature text. When you are finished entering the signature text, click Save to lock in the changes to your signature.