Click the "Start" button on your computer and hover over "All Programs." Click "Google Talk" to open the program. You can click on the Google Talks’ icon on your desktop as well.
Now Log on to Google Talk by using your current Gmail address (user name) and password.
Click “Settings” on the top of the Google Talk window.
Now, click “General” which is located on the left panel of the programme window.
Click “Account Settings” on the right panel in order to open the Google Account information page on your default web browser.
Now find the “Edit” option under “Personal Information.”
Think of a new Google Talk display name and type it in the "First Name" and "Last Name" boxes.
Click "Save" to save your new display name.
You are done! Your screen name on Google Talk has been successfully changed. Make sure you remember your new display name to use it the next time you log in to your Google Talk.
Do not forget to let your friends, family members and colleagues know that your Google Talk screen name has changed. This way, all of them will still know how to find you on Google Talk.