I haven't needed to do that on a Windows machine myself in ages, but I recall the Windows OS had built-in tools/control panels to do it some versions back. Those usually worked well, though not always the fastest. Sorry if I'm a bit behind the times re Windows tools, not having to do all the IT detail-work for several years now.
AND: Be sure the server is Down, no served files, when using it. I would think that any de-fragger software would stop all services before running, but it's worth confirming it. Could be worse than back-up software hitting live files if that was omitted.