@Reeve7
Let's our terms right first, so we're both talking about the same thing.
What you are talking about is "disk space" not "memory".
The disk is mapped into sections called partitions, and each one is assigned a letter. The "C":partition is usually the largest of the bunch and contains the OS, system files, and your Windows account files and settings. The "D" partition is most often the Recovery Drive and if you mess with that, you can't recover the PC anymore.
You need to go into the Disk Management tool and write down the information about the partitions and post that back here so we can provide you sound advice. To open that too, you enter "create and format" in the search area and then select Create and Format Hard Disk partitions.
Also, you can't simply transfer space from one partition to another. Instead, you have to shrink the larger partition to create some free space, and then expand the smaller partition to incorporate that space. This is done in Disk Management -- which is why we need the detail information.
***If my post helped, click the White
thumbs-up symbol to say thanks***
***Please mark
Accept As Solution if my post solved your problem***
I am a volunteer and I do not work for, nor represent, HP