Easeus partition magic free click here
Remember to backup all files.
Select the drive you want to reduce and click on resize/move, reduce size then click on apply. When this has completed Select C drive and increase the size then click on the apply button.
The reason for doing it one at a time is in case of a power glitch I had two yesterday closing down my computer.
You could also download Partition recovery just in case of a problem. click here