First of all we can download WSS3 stepup via
http://www.microsoft.com/en-us/download/details.aspx?id=7006Once setup is started,
1. please select Advanced installation
2. Select Web Front End installation and click on install
3. When installation is completed we will see installation complete screen. From here you can start configuring WSS3 on your server by launching SharePoint Products and Technologies configuration wizard.
Please goes through below attachments for better understanding.
