Back up all the important files by copying them on to an external hard disk, a DVD or an USB stick. This is essential because the process of uninstalling the Windows on your computer will involve formatting the whole computer, which means all contents in the computer will have to be deleted.
Insert the windows disk and follow the instructions to verify that the disk is bootable. Restart the computer, then wait for a message to appear on a dialogue box. A message bearing the instruction "Press any key to boot from CD or DVD" will prompt you to press any key. When the message appears, press any key on the keyboard, such as the enter key to initialize the rebooting process. The computer will start rebooting from the disc.
Press the designated key before the operating system is loaded, and while the computer is still in its boot process. The computer's boot menu will then appear on the screen prompting you to press the "R" button on the keyboard to enter the recovery console. Upon entering the recovery console, a black screen of the command prompt will appear: "C:\ WINDOWS>." At this point, key in "format c / fs:ntfs." A warning will then appear informing you that this will erase all contents of the hard drive. Key in the letter "Y" and press enter to commence the hard drive formatting.
Restart the computer and enter the disc of the new Windows you want to install, once the booting process is complete. The computer will automatically detect the disc. Follow the instructions on the screen to commence on the installation of the new windows.