At this point I'm still at a loss as to what you are wanting to do. I don't understand what you're trying to say in the title of this topic, as you're wide open as to how you could reconfigure the space taken up by C: at present.
Your drive looks perfectly fine. Your C: drive is virtually empty so if you wished you could shrink the partition size for C: down to, say, 200 GB which is a hair more than 20% of the total size of the current C: partition, unallocating the remainder, allowing C: to be strictly for Windows and installed programs. Then you could take that unallocated remainder and create a partition from it, assigning it a drive letter other than A, B, C, or D (and, if you have an optical drive, probably E). Of course, if you do this you also then need to tell Windows that your user folders and libraries need to be permanently moved to the new drive. It's been so long since I last did that that I've forgotten the details and would have to do a web search on the steps.
Of course, any time one is thinking about repartitioning a full system image backup as well as a separate user data backup should be taken before doing so. I haven't had an issue with repartitioning in many, many moons but if it fails, and you don't have backups, things get very ugly very quickly.
I far prefer third party tools for repartitioning because they're more user friendly and will allow you to take a look at how what you are doing will look once done. Most do not actually do anything until you give the final go, but can give you a preview of how what you propose to do will turn out. They also catch you if you try to shrink something "too small" for what's on it or expand beyond space available.
Brian AKA Bri the Tech Guy (website in my user profile) - Windows 10 Home, 64-Bit, Version 1803, Build 17134
In a modern society where everyone thinks their opinion deserves to be heard nothing annoys me more than individuals who mistake their personal preferences for fact.
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