1. Run setup.exe from a network location (installation directory).

2. Follow the wizard through to the Ready to Upgrade page. The path to the configuration file is specified in the Read to Upgrade page in the configuration file path section.

3. Cancel the setup without actually completing the installation, to generate the INI file.

4. Copy the ConfigurationFile.ini to the same folder of the installation directory.

5. Create a new file on the installation directory and name it upgrade.bat

6. Open upgrade.bat with Notepad and add the follow line: Setup.exe /ConfigurationFile=ConfigurationFile.ini

7. Open ConfigurationFile.ini with Notepad 

   1. Add this line to the beginning of the file after [SQLSERVER2008]: IAcceptSQLServerLicenseTerms="True"

   2. Change QUIETSIMPLE="False" to QUIETSIMPLE="True"

   3. Comment out this line: UIMODE="Normal" ->  ;UIMODE="Normal"

8. Save all files.

9. Double click on upgrade.bat will launch the upgrade process.

Reference: 

1. http://msdn.microsoft.com/en-us/library/dd239405.aspx
2. http://msdn.microsoft.com/en-us/library/ms144259.aspx