Fragmented files in your hard disk causes your computer to slow down to an extent. Because if we need to read from a fragmented file it needs more time for the computer to find that file. so defragmenting makes your pc works faster. you can do this by following these steps

Step 3 : Then Disk Defragmenter Window comes. then select the drive you want to defragment and click on Analyze to Analyze the disk selected or click on the Defragment Button to start the defragmentation process.