You don't need to buy software to obtain some extra disk space Windows has its own built in cleaner just double click on My Computer (or This PC for Win 8.1) then right click on the drive you want to clean, Click on Properties, and then on Disk Cleanup. You will be given a list of Files that can be removed. Click Here
Or a simpler method is to download the free version of CCleaner Click Here and it will guide you through cleaning unwanted files and also give you the option of cleaning the Registry. Disk defragmentation does not remove any files from your PC it just organises them in a more useful form.