I've been searching for 20 minutes and I can't a way to change it with regedit. If there are important files you need which you can move to the K drive, I would look into making an Ubuntu live CD/DVD
. As that page mentions, you can sometimes use a USB flash drive instead of a disc, but not all flash drives support it. The live CD is an operating system ran from a CD. You can't make any permanent changes to the Ubuntu OS, but you will have access to both hard drives.