It's possible and the option is called 'resize' if it appears in a partitioning program. The only thing is which filesystem you have. FAT resizes fine, NTFS usually too. Still, it's a complicated peration, so you should make a backup of your most important files before you try this. There are many programs that can do this. One of them is GParted: http://gparted.sourceforge.net/
(it may be also included in your system).