Download the drivers for the software first:
4shared.com - online file sharing and storage - download USBFlashDriver.zip

Then xs++:
4shared.com - online file sharing and storage - download XS++_V3.1_Darwin.rar

You could read abit about the software here:
XS++ 3.1 Guide-Flashing,Customizing,Recovering - Top Sony Forums

Now just follow this simple guide after u've got to know the software:
Top Sony Forums - View Single Post - How to use phone sx or xs++

Regards,