Unless you have unallocated space on the hard drive to extend a partition to (or create a new one), you will have to reformat it. Even doing so, you will need to use fdisk.exe from command prompt in order to delete the partition and create new ones. The only way you could do this is if your partitions were set to dynamic (using a third party tool) and then you would be able to change the size of them, but even then you risk data loss if you incorrectly adjust the memory allocation.

http://www.techyv.com/questions/my-system-hard-disk-not-working-properly