back up your data on another drive.
go to 'my computer', locate your hdd's drive letter. right click on the drive letter, from the right click drop down menu, choose 'format'. when format window comes up, select either quick format or leave it unchecked. wait for the format to complete.
you can do the same thing from disk management window. type disk manager in the start menu search box to find the disk manager.
Why would you want fat32 on a 500gb hd? You would be severely limiting its capabilities by formating it that way. NTFS allows for files larger than 4gb on it and Fat32 only allows 4gig and under files.