Fragmentation makes your hard disk do extra work that can slow down your computer. Disk Defragmenter rearranges fragmented data so your hard disk can work more efficiently. Disk Defragmenter runs on a schedule, but you can also defragment your hard disk manually.
Click on the Start button, then All Programs, then Accessories, then System Tools.
Click on Disk Defragmenter. If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
Note:
Here's another way to open Disk Defragmenter: Click the Start button. In the Search box, type Disk Defragmenter or defrag, and then, in the list of results, double-click Disk Defragmenter.
Click Defragment Now.
Disk Defragmenter might take from several minutes to a few hours to finish, depending on the size and degree of fragmentation of your hard disk. You can still use your computer during the defragmentation process.