Start by clicking on Start, All Programs, Accessories, System Tools, Disk Defragmenter.
Select c:/ drive and click on Analyze.
You'll see this pop up after it's analyzed your drive and suggests to defrag or not. Mine didn't need defragmented when I drafted this tutorial, but next you click on Defragment.
The next screen will show the progress as it defrags your disk.
When you see this popup, click on Close and you're done.