"although I was able to activate it, I am unable to upgrade."
Could you give more details on on this?
"Second, I don't see any VST plug-in tags in my studio one 5 location. What should I do?"
I would try the following.
Open Studio One - look in the ABOUT section. What you need to find is what version your computer says is installed. You could have the right upgrade on your account, but not fully upgraded on your computer.
Studio One 5 Artist has VSTi support included, Don't let others tell you different.
"With version 5, Studio One Artist now has built-in support for VST and AU plug-ins, ReWire, and Studio One Remote control software for iPad and Android tablets. These features were formerly available for Studio One Artist only as separate Add-ons.".
It could be as easy as just updating your software license for Studio One on your computer.