|1. In Disk Management, right-click the graphic of the D drive (20GB) and choose Delete Volume, giving unallocated space (you will lose any data stored there).|
2. Right-click the graphic of the C drive, choose Shrink Volume and the amount of space to shrink it by then click Shrink (make it at least 60GB in size, 45GB is marginally too small).
3. Right-click on the new unallocated space, click on New Simple Volume, give it a meaningful Volume Label and run a Quick format.
NOTE. When you Shrink C, it can only decrease the partition size down to the first unmovable/locked system file. Running a defragmentation may move some of the ‘unmovable’ files. Also, if you’re running System Restore, you could try temporarily turning it off, do the Shrink and turn it back on.