Microsoft has introduced a very unique method for the delivery of an OS update with the Windows 8.1 Preview and that is delivering it through the Windows Store.
The video below goes through the process of getting the required Windows Update which then prompts the Windows 8.1 update to be offered from the Windows Store for installation.
You will see that process all the way until the Start Screen appears.
Note: Some elements have been skipped or sped up to move the process along on the video. Too bad that is not possible in real life because the entire process takes about 75 minutes from start to finish.