Instructions needed for updating Information Manager from 1.7.3 to 1.8.7

My RDi was trashed and needs to be replaced. The remnants have been uninstallled from my PC (Win Vista Business). The SysAdmin is getting a new copy of RDi 9.5.? downloaded and unpacked now. My Installation Manager v1.7.3 needs to be upgraded, so I got v1.8.7 from Fix Central, and have unzipped to a folder on my PC.
I tried to define a repository specifying that folder (C:\Temp\Installs\IBM Installation Manager v1.8.7\) as the repository, but could not. Add Repository Error said that's not a repository - it's an install package. It also says to exit Installation Manager and execute the install from the Installation Package.

I looked through all the files and folders in that "Installation Package", but do not see any that I can "execute".
There is a readme.html in the documentation\en folder that says to refer to the "...installation guide for Installation Manager".
While that instruction did not have a link, I found what appeared to be applicable instructions in the KnowlegeCenter, and proceeded to the "To install Installation Manager" part of "Installing or updating Installation Manager silently by using the installer".

I'm now at https://www.ibm.com/support/knowledgecenter/SSDV2W_1.8.5/com.ibm.silentinstall12.doc/topics/t_silent_installIM_IMinst.html

I skipped ahead to steps 4, 5, and 6, but in Step 6 (where I use the "installc.exe -log [my log file] -acceptLicense" command), I'm told that "'installc.exe' is not recognized as an internal or external command, operable program, or batch file."

Am I in the wrong rabbit hole again?

Michael Koester
Programmer/Analyst