Given the following notional Git history:
A--B--C (origin/master) *dead branch*
\--D--E (working) *live branch, preferred master*
Is there any way to move origin/master to the working live branch, and keep on rolling? I'm very aware of "Why'd you let origin/master go dead? Don't do that", and I will carefully heed that advice in the future. But that's my current reality, and I'm asking for extraction advice.
Update 2019-08-22: Here's another very useful post if what you actually want to do is delete the remote master branch. I found @SlightlyCuban's answer to be most helpful here in non-GitHub situations where you have shell access to your remotes.
Also, deleting the local branch that's tracking the remote branch is explained well in this answer.