If you are using Windows XP or Vista or Windows 7 now you can upgrade your operatingsystem to windows 8. So this will overwrite with your earlier version of windows. So you have to install the software's once again.
1. Goto microsoft.com.Windows 8 Download page (Click Here) and download the ISO file and then make it as Bootable DVD using Windows 7 DVD / USB tool
2. If you already have the DVD of Windows 8 insert it in your computer.
3.Open The DVD Drive and double-click the setup.exe file
6. Accept the EULA and choose the component of your existing Windows setup that you like to preserve in Windows 8. You can either do a clean install and choose “Nothing” or use the “Windows settings, personal files and apps” option to preserve everything.
You have to reinstall certain apps after Windows 8 is installed. Also, if you choose “Nothing,” your personal files (anything saved inside the User folder and on the desktop) will be moved to a windows.old folder.
7. Windows 8 installer may want you to uninstall certain apps(Like - Microsoft Security Essentials). One you have done that, restart the PC and hit the Install button. You can re-install these apps once the installation is complete. Thats all.