Hello I'm Smart....
To defrag your HDD, depending on the Windows you are using, I will directing you using Window 8.
From your Computer *My Computer Icon* after you've opened it, you will see your hard drives, select the one in which your operating system runs on. Right click on it, Go to Properties and click.
From the information box, locate Tools and click. Locate Optimize Drives and click.
If you want to defragment your drive, click Optimize. It's best to do this when you don't need to use your computer for anything else, so you can let Windows defragment the drive efficiently.
You can decide to Analyse first, depending on the time you've got.
Thanks.