Can only use 2GB of a 40 GB HDD.

I recently upgraded to win2k, from win 98 on a HP Pavilion 8575c. I have a 40 gig hdd. But, I can only use 2 gig of hdd space. The present file sys if FAT 32. I’ve tried to convert to NTFS but unable to convert. I need to use the whole 40 GB ofthe HDD. How can I get the full size of the HDD?