There is a simple command-line tool that exists for such purpose called convert.
In order to convert one of your drives, click Start, then Run and type:
convert volume /fs:ntfs
where “volume” is a drive letter followed by colon, for example:
convert c: /fs:ntfs
If you are trying to convert a system drive, some files of which are being used by Windows, you may get the following message:
Convert cannot run because the volume is in use by another process
In this case, press Y and let your PC reboot. Conversion will take place at next startup.
If you are converting a volume, that is not currently used by any processes, you’ll see it converted to NTFS file system.