I had succesfully worked thru getting the Update process to work and then I had to change some code in one of my projects. Since it was small and did not change the size of the msi at all, I figured this must be a patch.
After downloading and installing the full Windows SDK for Windows 10, I was able to find to find the msimsp.exe file.
I saved the existing project, then saved the project again without generating a new product id as per the tutorial.
I set the external tool to use the msimsp file but it hangs midway thru.
None of the previous posts detail the solution for the problem.