Freeing up space in Windows (C:)

I am getting errors saying that I do not have any storage left, so I looked and my windows (C) drive is full ( 665MB free of 118 GB) but my DATA (D) drive still has a lot of storage space (876 GB free of 913 GB). I have changed the defaults to now save new things to (D) but I still need to move some things out of (C). I am worried that if I just drag and drop certain things from (C) to (D) I might lose something. I just want to make sure that it is safe before I mess something up. Any help/advice is appreciated.

Thanks

Welcome to TenForums @emorymcdougald

One thing you could easily move from C: to D: is your pagefile, it's normally at least as large as your installed memory. Go to Control Panel\System and Security\System and click Advanced system settings. Create a system managed page file on D: and set 'none' on C: (you may need a reboot). More in this Tutorial.
Virtual Memory Pagefile - Manage in Windows 10

Then you can have a look at what's using up the space on C: - if you haven't done so already, run Disk Clean-up and click its 'Clean up system files' button. Amongst other things, you'll probably find a lot of space can be released by cleaning 'Windows updates'.
Disk Cleanup - Open and Use in Windows 10

Those two actions should regain several GB on C: - if that's not enough for you at least it will give you breathing space to move other things at your leisure.

I'm going to assume that your C drive is an SSD. If so, this would be a great time to upgrade to a larger one. You can find 256 GB ones very cheap, and even get a great deal on a 500-512 GB, if you wanted to jump t that size.