Check this thread if you haven’t already.
As to installing VSTs. I’m guessing you’re on Windows, yeah? Many freeware VSTs will come as a .dll file (normally packed in a rar or zip) and all you need to do in uncompress these and move into the folder you are telling Renoise to look at work VSTs. Something like “C:\Program Files\VST Plugins” for example. Or the may be executable files that install themselves, in which case they will try and do pretty much that but it is worth trying to make sure you are always using the same folder as some .exes have slightly different folders set as standard/