A registration key is provided on the download page.
Note it down carefully or copy/paste it in the document (in Notepad for example).
You will be asked for it later. Click Next to start the download of Windows 8.
Two versions are available: 32-bit and 64-bit.
The downloaded version will be the same type as the operating system you are running.
Using the ISO image
Visit this page and download the version you want to install. Once the ISO image is downloaded, burn it to a DVD. For your information, if the download was performed on a computer running Windows 7, simply double-click on the ISO file to start burning procedure.
From the installer
Once the installer is downloaded, a dialog box prompts you to begin the installation.
Select Install Now to put Windows 8 on the active partition or install it on another partition.
Then click Next and follow the instructions given by the wizard.
From an ISO image burned on a DVD
Insert the DVD containing the ISO image in the drive and restart the computer.
Press a key when prompted to boot from the DVD.
Then simply follow the on-screen instructions to install Windows on the partition of your choice.