12/19/2012 Updates: If the machine you are updating has a 32 bit version of Windows, you're going to end up with a 32 bit version of Windows 8. When ordering from the Upgrade Assistant (below) you have no other choice. Someone said there may be a way to also upgrade from the 32 bit to 64 bit version at the same time for a slightly higher price, but I haven't explored this. Google it.
If you do the install in the existing partation (instead of an empty partition as I recommend) you're going to endup with both Windows 8 on your hard drive and your old version of Windows in a folder with a name like Windows.old ... as far as I know you don't need this, but you probably can't just delete it. See this discussion of deleting Windows.old folder. Option one, using Disk Cleanup looks pretty easy.
To get the upgrade to Windows 8 Professional for just $40, go to this site: windows.microsoft.com/en-US/windows/buy. You'll see:
Click on the "Download Pro" button and it will download a program called "Windows 8 Upgrade Assistant" which will check your machine for eligibility and compatibility. Be sure to run the program on the machine you want to upgrade. At the end it give you the ability to actually buy the Windows 8 Pro. This is where it gets a little tricky. What you want is to get the Program Key and the ISO file used for the installation. I'll provide more information on partitioning and actually doing the installation after I get my new laptop.
Once you install and run the Upgrade Assistant you'll see a screen which looks like this:
Be sure to click on the small type which says "See compatibility details" (arrow above). You'll see something like the:
Be sure to not only review the results before deciding to order, but I would recommend printing and/or saving as well.
After reviewing the results, click on Next (above). In order to do a clean install on a separate partition, choose "Nothing" on the next screen:
If you partition correctly and do a clean install, you won't loose anything ... it will be in the partition with your old version of Windows. However, my recommendation is to backup all you data to an external drive using SyncToy, and before partitioning, do a complete backup of your drive using a stand-alone program like Paragon.
Once you click "Next" (above) the next screen has the order button:
On the review order screen you can add a DVD, but assuming you can burn your own there is no need:
On the next screens you enter your Name and Address:
And your billing info:
Final check before you confirm your order:
Once you click the "Buy" button they process your order:
On the next screen you see the Key which you must not loose:
You can write it down. You can copy and paste it into a file and save it. You can click on "View Receipt" (link at bottom of screen above) which shows all the details including the Key and also has a "Print" button. And/or you can wait for an e-mail from them which will also have the Key ... by this time the e-mail has probably arrived, check your e-mail program.
If you click on Next the download will start, it make take a couple of hours:
Once the download is complete, it then takes some time to "getting files ready":
Choose "Install by creating media:"
Choose ISO file:
It will ask you where to put it and what to call it, don't forget where you put it. At that point it takes a while to actually create the ISO file:
In case you forget, it reminds you where the file is and what it was called, and if you click on the "Open DVD burner" it might even open your DVD burning program:
Once you've created the DVD and backed up all your data (and the system drive itself) and created a partition in which to install Windows 8 (or are willing to wipe out your existing system) follow these directions: pcsupport.about.com/od/windows-8/ss/windows-8-clean-install-part-1_2.htm
Also don't forget to get your free Key which adds Media Center back to Windows.
Good luck, and enjoy Windows 8!
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