You may be able to use
diskpart.exe
Note usage of the word
may in this excerpt from the link: (may interprets as "may or may not")
"Only the extension of data volumes is supported. System or boot volumes
may be blocked from being extended, and you
may receive the following error:
Diskpart failed to extend the volume. Please make sure the volume is valid for extending"
If it works, would be a better (simpler) alternative than using a third party partition program (one less thing to deal with)