Your c drive will probably hold your operating system so I do not recommend that you 'empty' this as it will stop your computer from working.
You can re-distribute the free space but this is complicated and I wouldn't recommend it unless you know what you are doing.
If your d drive is just holding movies then it will fill up very quickly as they take up lots of room. What you can do is just click on my computer, open your d drive, right click on any movie you have watched and scroll down to delete. It will then free up the space.
If you are brave and know what is on that drive - go to my computer, right click your d drive and then sroll down to format. It will then clean that drive and empty it. I would check first though that it only hold files you have saved and not any programs you want to keep.