Yes its very easy its called formatting the disc.
What you need to do is transfer the files you want to keep and then make sure that the PC is set to boot from the disc drive. This can be achieved from within the Bios, you need the boot options section of the bios. If you watch the PC when it boots it should tell you which key you need to press to get into the Bios. Look it up online and watch a video tutorial if it makes you feel easier about going into the Bios. take your time and read the pages carefully. its not as complicated and intimidating as it first looks.
Once you have the PC set to boot from the Disc drive, insert the OS disc and restart the PC. It will then boot to the OS disc and you will be given the option to format the disc before installing the new OS.
Mactronix