There are programs out there that let you modify partitions, though it's been years since I've had to use one. I know of two such programs that offer free "home" versions:
Partition Wizard and
Partition Master.
There are significant risks involved if you use one of these programs, and I would strongly recommend taking a backup of all your data before you do. Basically,
assume you're going to have to wipe the disk at some point, proceed as if you will, and enjoy the relief if you don't have to!
