To Update Windows:

Go To: http://www.windowsupdate.com

You will then see the following page:

Click on "Scan for updates"

If a window pops up asking you to install the Microsoft Update software, click yes

Then, Windows Update will scan your computer for any available updates.

In this particular scenario, I have no updates to install. But if there are updates, the section under "Critical Updates and Service Packs" will be in bold.

Click on "Critical Updates and Service Packs".

Again, in this particular scenario, there are no updates to install. But if you do, click on "Review and install updates" and follow the onscreen instructions.

At the end, windows will ask you to reboot your computer. Save all your current work and exit your programs before rebooting.

After rebooting, repeat this entire process (i.e. go back to www.windowsupdate.com) and check to see if there are any more critical updates to install. If there aren't any more, then you're done!