how to reinstall windows 8 on bootcamp

Start Bootcamp Assistant then select the option to remove Windows and return your drive to a single partition. Once Windows is removed start Bootcamp Assistant again and select the option to install Windows. Follow the Bootcamp instructions for installing Windows.

This process will not cause lose of OSx data or applications if done correctly. But as allways, create a good backup of your data because things sometimes go wrong or instructions are not followed causing data lose.