I am trying to remove junk from my C: drive. Do I need to save anything under IMatch5 or IMatch6? Help tells me I'm using IM2017
Which folders do you mean exactly?
If you uninstall IMatch 5 from the Control Panel (Add/Remove Software) everything that can be uninstalled is uninstalled.
OK, I should have known that. Is IMatch6 equivalent to IM2017?
Yes.
You can delete the %PROGRAMDATA%\photools.com\IMatch5 folder to save a few extra KB.
But before make sure that IMatch is not using this folder for your settings database (Edit > Preferences > Application) or any of the Presets folders.