If you're using Git on Windows, follow these steps:

1. Open the Start Menu and search for Credential Manager, then open it.

2. Select the Windows Credentials tab.

3. Scroll down and look for entries related to GitHub.

4. If there are multiple entries with different usernames, identify the one you need to remove.

5. Click on the entry to expand it, then select Remove.

6. Confirm the removal when prompted.