I am pretty sure you cannot do it within windows, but there are plenty of partition manager programs out there to do it. GParted is old as dirt, and should still be solid.
http://gparted.sourceforge.net/livecd.php
Follow the directions or whatever, burn it to disk or USB, and boot your computer with it. May take a while to run and do its shit, but whatever. Should work. Lets you resize, delete, move & create partitions.
Also, as far as tracking down what's taking up all that room on your drives, this program is pretty awesome. http://windirstat.info/ Run it on a drive, and it will show you statistically and with color-coded blocks sized proportionally to the files on your drives. Makes it VERY easy to see where huge files are hiding.