I bought a larger SSD (256G to replace 128G), used a stand-alone disk duplicator to clone the old drive to the new, and found when I booted up the new drive, that it was limited to 128 (with another 128 "unallocated"). And Windows Disk Manager had "extend" volume grayed out, even though the unallocated space was to the right of the allocated.

Fretted and experimented a bit--then found your instructions. Option Two (using DISKPART) worked . . . and worked instantaneously! Bang! I have 256G on C:.

Thank you so much. I consider myself very computer savvy, but I did not know about DISKPART.