this is what you need to do
1) go to the start menu then right click computer and click manage
2) on the left hand side, you got storage, and under that disk management. click on disk management
3) on the bottom of the screen you will notice all the drive partitions availablre.
4) right click on d and hit shrink volume. this will take some time depending on how big your partition is
5) Input the amount you want to partition, this will create a new partition.
6) Once thats done, right click on your c drive and select extend volume
7) click on the newly created partition and now you have successfully extended your c drive.
Hope this helps