Hi avitesh, If your system is running absolutely fine without any problems then you do not need to reinstall the Windows to create partitions. You can create partitions from a program called Disk Management present in Windows itself. To know how to create partitions using Disk Management in Windows 8, click here  Hope this helps.  
Hello,       Recently i purchased Dell inspiron 15 (i5, 1TB HD, 4 GB RAM) with windows 8. I want to make the partitions on the harddisk and reinstall the operating system (windows 8). How can i reinstall the OS again. Please suggest.  Thanks   
Re-installation of OS