Backing-up the data on the drive to be manipulated is suggested as a matter of abundant caution.
Resizing/Formatting a large drive obviously is going to take some time. If there is a sudden power outage and if your UPS does not have sufficient runtime to complete the operation or there is any other mishap that results in its interruption, all your data will be lost/corrupted.
If you are willing to take the risk, by all means go ahead and resize the NTFS partition using Windows 7 Disk Management and then use my tutorial to format the rest of the drive to FAT32.
No need to download a large-sized partitioning utility. guiformat.exe that can accomplish the FAT 32 formatting in a jiffy, is just a 72 KB file.
OR
Wait for another 'Right off the assembly line' to appear here and 'copy/paste' a tutorial from elsewhere.