A couple of things you can try:
- move the Swap file to D:, using Control Panel / System, Advanced tab. Since C: and D: are on the same physical drive, don't enable it on both. (If you had two separate physical drives, you could.)
- run Cleanup Manager (cleanmgr) and see what it can do. It can clean off temporary files from installations etc.
- check how much space is used by System Recovery - maybe you can lower that to free up space