Convert from fat32 to ntfs:

From the command line: CONVERT C: /FS:NTFS

However, the best way in my opinion is a 3rd party product such as Partition Magic (version 7.0 or later). Lets you do everything from within the GUI and it's a delight to work with. Without Partition Magic, this is a one-way process (you cannot convert back to FAT without a reformat)