To change your computer username, you can follow these steps:

1. On Windows:
- Go to Control Panel > User Accounts > User Accounts.
- Click on "Change your account name" and follow the prompts to change your username.

2. On Mac:
- Go to System Preferences > Users & Groups.
- Click on the lock icon and enter your password to ke changes.
- Right-click on your username and select "Advanced Options."
- Change the "Account name" field to update your username.

3. On Linux:
- Open a terminal window.
- Use the `usermod` com nd to change the username. For example:
```bash
sudo usermod -l new_username old_username
```
- You y also need to change the home directory name using the `-d` option.

Remember to log out and back in after changing your username for the changes to take effect.