The usual method is to copy the files out, delete the partition, create it again but to make it FAT32. Then copy the files back.
There is Partition Magic but that's going to cost a few dollars and I've seen it lose all the files even when it said it was going to be fine.
Can you share why you want an old unreliable file system?
The OS of my laptop is wXPpro on partition C:. Partition D: is for my own files. The FS of them are NTFS.
Now I want to change the FS of D: from NTFS to Fat32, what are the ways?
Could you tell me?