How can I move space from the (D:) to the (C:) to give me more space?

[sigulem]

Hi,

I have installed WinToUSB on a 128gb USB 3.0 SanSisk.

Here is what I have:
WinToUSB (C - 657 MB free of 19.9 GB
WinToUSB (D - 81.6 GB free of 115.7 GB

It seems every app I install and all of the Windows updates are eating up the (C virtual drive and eventually I won't have any space left.

Disk Management says I have this
Disk1: WinToUSB (D 115.7 GB NTSF - Healthy (System, Active, Primary Partition)
Disk2: Win10 (C 19.99 GB NTFS - Healthy (Boot, Active, Crash Dump, Primary Partition)

Q:  How can I move space from the (D to the (C to give me more space?